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 $65.65   5.243%   $69.092   $69.09   $69.10   $69.10  
  Purchase #2 $220.67   5.441%   $232.6767   $232.68   $232.70   $232.70  
  Purchase #3 $147.73   8.706%   $160.5914   $160.59   $160.60   $160.60  
  Purchase #4 $176.70   11.171%   $196.4392   $196.44   $196.45   $196.40  
  Purchase #5 $74.66   9.859%   $82.0207   $82.02   $82.00   $82.00  
  Purchase #6 $157.32   11.729%   $175.7721   $175.77   $175.75   $175.80  
  Purchase #7 $83.90   5.207%   $88.2687   $88.27   $88.25   $88.30  
  7 purchase totals = $926.63       $1,004.8608   $1,004.86   $1,004.85   $1,004.90