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 $245.26   6.229%   $260.5372   $260.54   $260.55   $260.50  
  Purchase #2 $140.52   5.658%   $148.4706   $148.47   $148.45   $148.50  
  Purchase #3 $47.26   13.516%   $53.6477   $53.65   $53.65   $53.60  
  Purchase #4 $220.69   5.812%   $233.5165   $233.52   $233.50   $233.50  
  Purchase #5 $240.94   4.761%   $252.4112   $252.41   $252.40   $252.40  
  Purchase #6 $213.78   3.865%   $222.0426   $222.04   $222.05   $222.00  
  Purchase #7 $58.86   10.644%   $65.1251   $65.13   $65.15   $65.10  
  7 purchase totals = $1,167.31       $1,235.7509   $1,235.76   $1,235.75   $1,235.60