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 $246.91   11.659%   $275.6972   $275.70   $275.70   $275.70  
  Purchase #2 $146.78   4.524%   $153.4203   $153.42   $153.40   $153.40  
  Purchase #3 $52.26   12.271%   $58.6728   $58.67   $58.65   $58.70  
  Purchase #4 $197.99   12.223%   $222.1903   $222.19   $222.20   $222.20  
  Purchase #5 $187.45   7.228%   $200.9989   $201.00   $201.00   $201.00  
  Purchase #6 $5.78   9.549%   $6.3319   $6.33   $6.35   $6.30  
  Purchase #7 $56.59   5.864%   $59.9084   $59.91   $59.90   $59.90  
  7 purchase totals = $893.76       $977.2198   $977.22   $977.20   $977.20