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 $246.60   8.404%   $267.3243   $267.32   $267.30   $267.30  
  Purchase #2 $243.86   9.312%   $266.5682   $266.57   $266.55   $266.60  
  Purchase #3 $45.46   7.511%   $48.8745   $48.87   $48.85   $48.90  
  Purchase #4 $250.74   9.788%   $275.2824   $275.28   $275.30   $275.30  
  Purchase #5 $101.50   13.829%   $115.5364   $115.54   $115.55   $115.50  
  Purchase #6 $189.38   12.271%   $212.6188   $212.62   $212.60   $212.60  
  Purchase #7 $81.96   4.272%   $85.4613   $85.46   $85.45   $85.50  
  7 purchase totals = $1,159.50       $1,271.6659   $1,271.66   $1,271.60   $1,271.70