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 $182.65   13.318%   $206.9753   $206.98   $207.00   $207.00  
  Purchase #2 $50.77   12.592%   $57.163   $57.16   $57.15   $57.20  
  Purchase #3 $139.78   11.620%   $156.0224   $156.02   $156.00   $156.00  
  Purchase #4 $240.97   6.576%   $256.8162   $256.82   $256.80   $256.80  
  Purchase #5 $236.71   12.233%   $265.6667   $265.67   $265.65   $265.70  
  Purchase #6 $217.59   4.765%   $227.9582   $227.96   $227.95   $228.00  
  Purchase #7 $133.53   5.225%   $140.5069   $140.51   $140.50   $140.50  
  7 purchase totals = $1,202.00       $1,311.1087   $1,311.12   $1,311.05   $1,311.20