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 $88.51   5.516%   $93.3922   $93.39   $93.40   $93.40  
  Purchase #2 $10.99   6.423%   $11.6959   $11.70   $11.70   $11.70  
  Purchase #3 $23.62   10.504%   $26.101   $26.10   $26.10   $26.10  
  Purchase #4 $215.33   3.117%   $222.0418   $222.04   $222.05   $222.00  
  Purchase #5 $28.91   11.718%   $32.2977   $32.30   $32.30   $32.30  
  Purchase #6 $213.90   5.804%   $226.3148   $226.31   $226.30   $226.30  
  Purchase #7 $100.72   3.435%   $104.1797   $104.18   $104.20   $104.20  
  7 purchase totals = $681.98       $716.0231   $716.02   $716.05   $716.00