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 $176.53   11.267%   $196.4196   $196.42   $196.40   $196.40  
  Purchase #2 $180.50   6.338%   $191.9401   $191.94   $191.95   $191.90  
  Purchase #3 $187.86   7.265%   $201.508   $201.51   $201.50   $201.50  
  Purchase #4 $71.75   4.550%   $75.0146   $75.01   $75.00   $75.00  
  Purchase #5 $56.90   5.653%   $60.1166   $60.12   $60.10   $60.10  
  Purchase #6 $208.48   12.728%   $235.0153   $235.02   $235.00   $235.00  
  Purchase #7 $76.87   8.674%   $83.5377   $83.54   $83.55   $83.50  
  7 purchase totals = $958.89       $1,043.5519   $1,043.56   $1,043.50   $1,043.40