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 $69.88   4.682%   $73.1518   $73.15   $73.15   $73.20  
  Purchase #2 $246.78   11.557%   $275.3004   $275.30   $275.30   $275.30  
  Purchase #3 $16.43   4.785%   $17.2162   $17.22   $17.20   $17.20  
  Purchase #4 $65.78   4.124%   $68.4928   $68.49   $68.50   $68.50  
  Purchase #5 $155.96   4.646%   $163.2059   $163.21   $163.20   $163.20  
  Purchase #6 $97.59   12.870%   $110.1498   $110.15   $110.15   $110.10  
  Purchase #7 $190.41   4.389%   $198.7671   $198.77   $198.75   $198.80  
  7 purchase totals = $842.83       $906.2840   $906.29   $906.25   $906.30