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 $53.47   5.457%   $56.3879   $56.39   $56.40   $56.40  
  Purchase #2 $128.33   3.433%   $132.7356   $132.74   $132.75   $132.70  
  Purchase #3 $235.71   13.561%   $267.6746   $267.67   $267.65   $267.70  
  Purchase #4 $81.37   9.172%   $88.8333   $88.83   $88.85   $88.80  
  Purchase #5 $89.96   3.187%   $92.827   $92.83   $92.85   $92.80  
  Purchase #6 $30.89   10.134%   $34.0204   $34.02   $34.00   $34.00  
  Purchase #7 $53.38   12.737%   $60.179   $60.18   $60.20   $60.20  
  7 purchase totals = $673.11       $732.6578   $732.66   $732.70   $732.60