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 $189.35   8.867%   $206.1397   $206.14   $206.15   $206.10  
  Purchase #2 $65.55   9.163%   $71.5563   $71.56   $71.55   $71.60  
  Purchase #3 $171.42   10.253%   $188.9957   $189.00   $189.00   $189.00  
  Purchase #4 $76.29   10.814%   $84.54   $84.54   $84.55   $84.50  
  Purchase #5 $42.62   12.574%   $47.979   $47.98   $48.00   $48.00  
  Purchase #6 $120.74   10.226%   $133.0869   $133.09   $133.10   $133.10  
  Purchase #7 $33.83   9.427%   $37.0192   $37.02   $37.00   $37.00  
  7 purchase totals = $699.80       $769.3168   $769.33   $769.35   $769.30