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 $218.99   8.282%   $237.1268   $237.13   $237.15   $237.10  
  Purchase #2 $134.75   8.326%   $145.9693   $145.97   $145.95   $146.00  
  Purchase #3 $219.85   4.546%   $229.8444   $229.84   $229.85   $229.80  
  Purchase #4 $240.45   6.272%   $255.531   $255.53   $255.55   $255.50  
  Purchase #5 $75.96   8.544%   $82.45   $82.45   $82.45   $82.50  
  Purchase #6 $236.98   4.300%   $247.1701   $247.17   $247.15   $247.20  
  Purchase #7 $235.53   9.669%   $258.3034   $258.30   $258.30   $258.30  
  7 purchase totals = $1,362.51       $1,456.3950   $1,456.39   $1,456.40   $1,456.40