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 $67.67   11.325%   $75.3336   $75.33   $75.35   $75.30  
  Purchase #2 $173.50   11.361%   $193.2113   $193.21   $193.20   $193.20  
  Purchase #3 $41.63   11.183%   $46.2855   $46.29   $46.30   $46.30  
  Purchase #4 $167.65   3.793%   $174.009   $174.01   $174.00   $174.00  
  Purchase #5 $116.35   6.402%   $123.7987   $123.80   $123.80   $123.80  
  Purchase #6 $188.32   9.447%   $206.1106   $206.11   $206.10   $206.10  
  Purchase #7 $159.38   9.314%   $174.2247   $174.22   $174.20   $174.20  
  7 purchase totals = $914.50       $992.9734   $992.97   $992.95   $992.90