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 $209.72   6.811%   $224.004   $224.00   $224.00   $224.00  
  Purchase #2 $14.47   7.326%   $15.5301   $15.53   $15.55   $15.50  
  Purchase #3 $33.56   5.865%   $35.5283   $35.53   $35.55   $35.50  
  Purchase #4 $207.54   5.509%   $218.9734   $218.97   $218.95   $219.00  
  Purchase #5 $93.79   13.115%   $106.0906   $106.09   $106.10   $106.10  
  Purchase #6 $63.73   3.236%   $65.7923   $65.79   $65.80   $65.80  
  Purchase #7 $229.52   11.717%   $256.4129   $256.41   $256.40   $256.40  
  7 purchase totals = $852.33       $922.3316   $922.32   $922.35   $922.30