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 $78.54   5.377%   $82.7631   $82.76   $82.75   $82.80  
  Purchase #2 $161.50   5.849%   $170.9461   $170.95   $170.95   $170.90  
  Purchase #3 $56.68   6.388%   $60.3007   $60.30   $60.30   $60.30  
  Purchase #4 $202.75   8.262%   $219.5012   $219.50   $219.50   $219.50  
  Purchase #5 $14.63   12.438%   $16.4497   $16.45   $16.45   $16.40  
  Purchase #6 $60.94   5.369%   $64.2119   $64.21   $64.20   $64.20  
  Purchase #7 $243.43   12.736%   $274.4332   $274.43   $274.45   $274.40  
  7 purchase totals = $818.47       $888.6059   $888.60   $888.60   $888.50