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 $250.48   4.350%   $261.3759   $261.38   $261.40   $261.40  
  Purchase #2 $143.83   4.828%   $150.7741   $150.77   $150.75   $150.80  
  Purchase #3 $118.35   3.558%   $122.5609   $122.56   $122.55   $122.60  
  Purchase #4 $26.65   6.805%   $28.4635   $28.46   $28.45   $28.50  
  Purchase #5 $158.26   10.436%   $174.776   $174.78   $174.80   $174.80  
  Purchase #6 $119.86   3.467%   $124.0155   $124.02   $124.00   $124.00  
  Purchase #7 $149.83   13.743%   $170.4211   $170.42   $170.40   $170.40  
  7 purchase totals = $967.26       $1,032.3870   $1,032.39   $1,032.35   $1,032.50