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 $92.66   6.221%   $98.4244   $98.42   $98.40   $98.40  
  Purchase #2 $205.35   3.459%   $212.4531   $212.45   $212.45   $212.50  
  Purchase #3 $14.96   13.526%   $16.9835   $16.98   $17.00   $17.00  
  Purchase #4 $233.53   4.441%   $243.9011   $243.90   $243.90   $243.90  
  Purchase #5 $229.66   13.331%   $260.276   $260.28   $260.30   $260.30  
  Purchase #6 $59.30   7.555%   $63.7801   $63.78   $63.80   $63.80  
  Purchase #7 $235.73   6.287%   $250.5503   $250.55   $250.55   $250.60  
  7 purchase totals = $1,071.19       $1,146.3685   $1,146.36   $1,146.40   $1,146.50