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 $206.29   3.486%   $213.4813   $213.48   $213.50   $213.50  
  Purchase #2 $16.41   3.195%   $16.9343   $16.93   $16.95   $16.90  
  Purchase #3 $221.36   7.369%   $237.672   $237.67   $237.65   $237.70  
  Purchase #4 $207.97   11.796%   $232.5021   $232.50   $232.50   $232.50  
  Purchase #5 $180.53   3.299%   $186.4857   $186.49   $186.50   $186.50  
  Purchase #6 $44.42   5.723%   $46.9622   $46.96   $46.95   $47.00  
  Purchase #7 $144.31   4.447%   $150.7275   $150.73   $150.75   $150.70  
  7 purchase totals = $1,021.29       $1,084.7651   $1,084.76   $1,084.80   $1,084.80