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 $124.70   13.136%   $141.0806   $141.08   $141.10   $141.10  
  Purchase #2 $185.54   9.215%   $202.6375   $202.64   $202.65   $202.60  
  Purchase #3 $56.73   9.668%   $62.2147   $62.21   $62.20   $62.20  
  Purchase #4 $178.89   13.741%   $203.4713   $203.47   $203.45   $203.50  
  Purchase #5 $66.88   12.352%   $75.141   $75.14   $75.15   $75.10  
  Purchase #6 $108.75   13.194%   $123.0985   $123.10   $123.10   $123.10  
  Purchase #7 $82.87   9.780%   $90.9747   $90.97   $90.95   $91.00  
  7 purchase totals = $804.36       $898.6183   $898.61   $898.60   $898.60