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 $186.98   11.677%   $208.8137   $208.81   $208.80   $208.80  
  Purchase #2 $230.35   10.410%   $254.3294   $254.33   $254.35   $254.30  
  Purchase #3 $232.78   5.664%   $245.9647   $245.96   $245.95   $246.00  
  Purchase #4 $107.66   8.484%   $116.7939   $116.79   $116.80   $116.80  
  Purchase #5 $183.74   12.618%   $206.9243   $206.92   $206.90   $206.90  
  Purchase #6 $200.78   8.511%   $217.8684   $217.87   $217.85   $217.90  
  Purchase #7 $181.54   11.405%   $202.2446   $202.24   $202.25   $202.20  
  7 purchase totals = $1,323.83       $1,452.9390   $1,452.92   $1,452.90   $1,452.90