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 $112.78   11.745%   $126.026   $126.03   $126.05   $126.00  
  Purchase #2 $152.83   10.772%   $169.2928   $169.29   $169.30   $169.30  
  Purchase #3 $107.93   10.823%   $119.6113   $119.61   $119.60   $119.60  
  Purchase #4 $231.65   9.267%   $253.117   $253.12   $253.10   $253.10  
  Purchase #5 $127.31   4.591%   $133.1548   $133.15   $133.15   $133.20  
  Purchase #6 $37.72   5.457%   $39.7784   $39.78   $39.80   $39.80  
  Purchase #7 $126.96   6.348%   $135.0194   $135.02   $135.00   $135.00  
  7 purchase totals = $897.18       $975.9997   $976.00   $976.00   $976.00