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 $67.75   13.522%   $76.9112   $76.91   $76.90   $76.90  
  Purchase #2 $142.74   10.360%   $157.5279   $157.53   $157.55   $157.50  
  Purchase #3 $246.31   6.791%   $263.0369   $263.04   $263.05   $263.00  
  Purchase #4 $246.56   13.111%   $278.8865   $278.89   $278.90   $278.90  
  Purchase #5 $237.52   12.208%   $266.5164   $266.52   $266.50   $266.50  
  Purchase #6 $196.76   5.226%   $207.0427   $207.04   $207.05   $207.00  
  Purchase #7 $43.53   6.495%   $46.3573   $46.36   $46.35   $46.40  
  7 purchase totals = $1,181.17       $1,296.2789   $1,296.29   $1,296.30   $1,296.20