Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.36   6.148%   $195.6945   $195.69   $195.70   $195.70  
  Purchase #2 $195.70   13.175%   $221.4835   $221.48   $221.50   $221.50  
  Purchase #3 $123.61   12.257%   $138.7609   $138.76   $138.75   $138.80  
  Purchase #4 $209.34   12.441%   $235.384   $235.38   $235.40   $235.40  
  Purchase #5 $148.99   8.745%   $162.0192   $162.02   $162.00   $162.00  
  Purchase #6 $159.25   11.138%   $176.9873   $176.99   $177.00   $177.00  
  Purchase #7 $106.95   10.481%   $118.1594   $118.16   $118.15   $118.20  
  7 purchase totals = $1,128.20       $1,248.4888   $1,248.48   $1,248.50   $1,248.60