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 $64.70   9.676%   $70.9604   $70.96   $70.95   $71.00  
  Purchase #2 $190.91   10.527%   $211.0071   $211.01   $211.00   $211.00  
  Purchase #3 $84.85   11.549%   $94.6493   $94.65   $94.65   $94.60  
  Purchase #4 $26.45   8.477%   $28.6922   $28.69   $28.70   $28.70  
  Purchase #5 $224.37   4.496%   $234.4577   $234.46   $234.45   $234.50  
  Purchase #6 $124.60   11.482%   $138.9066   $138.91   $138.90   $138.90  
  Purchase #7 $24.33   8.126%   $26.3071   $26.31   $26.30   $26.30  
  7 purchase totals = $740.21       $804.9804   $804.99   $804.95   $805.00