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 $58.80   13.626%   $66.8121   $66.81   $66.80   $66.80  
  Purchase #2 $248.72   5.346%   $262.0166   $262.02   $262.00   $262.00  
  Purchase #3 $46.63   8.257%   $50.4802   $50.48   $50.50   $50.50  
  Purchase #4 $107.93   8.243%   $116.8267   $116.83   $116.85   $116.80  
  Purchase #5 $88.35   9.560%   $96.7963   $96.80   $96.80   $96.80  
  Purchase #6 $51.98   8.603%   $56.4518   $56.45   $56.45   $56.50  
  Purchase #7 $192.74   4.797%   $201.9857   $201.99   $202.00   $202.00  
  7 purchase totals = $795.15       $851.3694   $851.38   $851.40   $851.40