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 $235.71   7.346%   $253.0253   $253.03   $253.05   $253.00  
  Purchase #2 $193.96   6.131%   $205.8517   $205.85   $205.85   $205.90  
  Purchase #3 $229.87   10.303%   $253.5535   $253.55   $253.55   $253.60  
  Purchase #4 $93.97   7.678%   $101.185   $101.19   $101.20   $101.20  
  Purchase #5 $197.28   11.357%   $219.6851   $219.69   $219.70   $219.70  
  Purchase #6 $191.95   4.692%   $200.9563   $200.96   $200.95   $201.00  
  Purchase #7 $51.36   4.307%   $53.5721   $53.57   $53.55   $53.60  
  7 purchase totals = $1,194.10       $1,287.8290   $1,287.84   $1,287.85   $1,288.00