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 $182.61   13.438%   $207.1491   $207.15   $207.15   $207.10  
  Purchase #2 $226.57   5.137%   $238.2089   $238.21   $238.20   $238.20  
  Purchase #3 $86.55   7.366%   $92.9253   $92.93   $92.95   $92.90  
  Purchase #4 $54.49   13.437%   $61.8118   $61.81   $61.80   $61.80  
  Purchase #5 $45.53   10.482%   $50.3025   $50.30   $50.30   $50.30  
  Purchase #6 $131.77   12.287%   $147.9606   $147.96   $147.95   $148.00  
  Purchase #7 $24.42   5.288%   $25.7113   $25.71   $25.70   $25.70  
  7 purchase totals = $751.94       $824.0695   $824.07   $824.05   $824.00