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 $31.29   6.487%   $33.3198   $33.32   $33.30   $33.30  
  Purchase #2 $246.43   10.580%   $272.5023   $272.50   $272.50   $272.50  
  Purchase #3 $148.29   3.371%   $153.2889   $153.29   $153.30   $153.30  
  Purchase #4 $145.61   11.732%   $162.693   $162.69   $162.70   $162.70  
  Purchase #5 $61.83   10.335%   $68.2201   $68.22   $68.20   $68.20  
  Purchase #6 $132.48   12.457%   $148.983   $148.98   $149.00   $149.00  
  Purchase #7 $247.42   3.741%   $256.676   $256.68   $256.70   $256.70  
  7 purchase totals = $1,013.35       $1,095.6831   $1,095.68   $1,095.70   $1,095.70