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 $213.85   13.358%   $242.4161   $242.42   $242.40   $242.40  
  Purchase #2 $198.57   4.258%   $207.0251   $207.03   $207.05   $207.00  
  Purchase #3 $62.75   3.516%   $64.9563   $64.96   $64.95   $65.00  
  Purchase #4 $48.93   11.232%   $54.4258   $54.43   $54.45   $54.40  
  Purchase #5 $60.61   8.730%   $65.9013   $65.90   $65.90   $65.90  
  Purchase #6 $48.98   4.490%   $51.1792   $51.18   $51.20   $51.20  
  Purchase #7 $25.59   13.797%   $29.1207   $29.12   $29.10   $29.10  
  7 purchase totals = $659.28       $715.0245   $715.04   $715.05   $715.00