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 $87.44   10.131%   $96.2985   $96.30   $96.30   $96.30  
  Purchase #2 $76.69   11.253%   $85.3199   $85.32   $85.30   $85.30  
  Purchase #3 $111.76   11.145%   $124.2157   $124.22   $124.20   $124.20  
  Purchase #4 $106.71   5.270%   $112.3336   $112.33   $112.35   $112.30  
  Purchase #5 $200.86   3.666%   $208.2235   $208.22   $208.20   $208.20  
  Purchase #6 $229.60   11.676%   $256.4081   $256.41   $256.40   $256.40  
  Purchase #7 $8.70   8.739%   $9.4603   $9.46   $9.45   $9.50  
  7 purchase totals = $821.76       $892.2596   $892.26   $892.20   $892.20