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 $46.98   3.716%   $48.7258   $48.73   $48.75   $48.70  
  Purchase #2 $136.78   11.652%   $152.7176   $152.72   $152.70   $152.70  
  Purchase #3 $36.62   7.757%   $39.4606   $39.46   $39.45   $39.50  
  Purchase #4 $247.40   10.848%   $274.238   $274.24   $274.25   $274.20  
  Purchase #5 $140.68   7.244%   $150.8709   $150.87   $150.85   $150.90  
  Purchase #6 $59.48   8.762%   $64.6916   $64.69   $64.70   $64.70  
  Purchase #7 $159.92   3.542%   $165.5844   $165.58   $165.60   $165.60  
  7 purchase totals = $827.86       $896.2889   $896.29   $896.30   $896.30