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 $56.34   10.365%   $62.1796   $62.18   $62.20   $62.20  
  Purchase #2 $239.38   5.597%   $252.7781   $252.78   $252.80   $252.80  
  Purchase #3 $18.90   7.166%   $20.2544   $20.25   $20.25   $20.30  
  Purchase #4 $137.59   12.355%   $154.5892   $154.59   $154.60   $154.60  
  Purchase #5 $124.90   5.726%   $132.0518   $132.05   $132.05   $132.10  
  Purchase #6 $216.37   8.179%   $234.0669   $234.07   $234.05   $234.10  
  Purchase #7 $150.26   13.345%   $170.3122   $170.31   $170.30   $170.30  
  7 purchase totals = $943.74       $1,026.2322   $1,026.23   $1,026.25   $1,026.40