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 $75.67   11.793%   $84.5938   $84.59   $84.60   $84.60  
  Purchase #2 $132.42   6.802%   $141.4272   $141.43   $141.45   $141.40  
  Purchase #3 $85.40   9.809%   $93.7769   $93.78   $93.80   $93.80  
  Purchase #4 $196.32   13.134%   $222.1047   $222.10   $222.10   $222.10  
  Purchase #5 $219.29   8.302%   $237.4955   $237.50   $237.50   $237.50  
  Purchase #6 $58.60   9.463%   $64.1453   $64.15   $64.15   $64.10  
  Purchase #7 $117.94   11.496%   $131.4984   $131.50   $131.50   $131.50  
  7 purchase totals = $885.64       $975.0418   $975.05   $975.10   $975.00