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 $64.35   6.518%   $68.5443   $68.54   $68.55   $68.50  
  Purchase #2 $167.83   11.499%   $187.1288   $187.13   $187.15   $187.10  
  Purchase #3 $214.32   5.361%   $225.8097   $225.81   $225.80   $225.80  
  Purchase #4 $57.26   12.781%   $64.5784   $64.58   $64.60   $64.60  
  Purchase #5 $25.65   8.294%   $27.7774   $27.78   $27.80   $27.80  
  Purchase #6 $119.70   12.760%   $134.9737   $134.97   $134.95   $135.00  
  Purchase #7 $37.69   10.106%   $41.499   $41.50   $41.50   $41.50  
  7 purchase totals = $686.80       $750.3113   $750.31   $750.35   $750.30