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 $231.90   13.762%   $263.8141   $263.81   $263.80   $263.80  
  Purchase #2 $207.79   11.806%   $232.3217   $232.32   $232.30   $232.30  
  Purchase #3 $249.54   8.148%   $269.8725   $269.87   $269.85   $269.90  
  Purchase #4 $227.75   8.178%   $246.3754   $246.38   $246.40   $246.40  
  Purchase #5 $232.53   12.473%   $261.5335   $261.53   $261.55   $261.50  
  Purchase #6 $13.38   12.130%   $15.003   $15.00   $15.00   $15.00  
  Purchase #7 $204.84   3.307%   $211.6141   $211.61   $211.60   $211.60  
  7 purchase totals = $1,367.73       $1,500.5343   $1,500.52   $1,500.50   $1,500.50