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 $84.71   3.763%   $87.8976   $87.90   $87.90   $87.90  
  Purchase #2 $230.85   13.296%   $261.5438   $261.54   $261.55   $261.50  
  Purchase #3 $146.94   7.614%   $158.128   $158.13   $158.15   $158.10  
  Purchase #4 $197.58   10.683%   $218.6875   $218.69   $218.70   $218.70  
  Purchase #5 $205.52   11.196%   $228.53   $228.53   $228.55   $228.50  
  Purchase #6 $227.29   11.554%   $253.5511   $253.55   $253.55   $253.60  
  Purchase #7 $157.60   11.700%   $176.0392   $176.04   $176.05   $176.00  
  7 purchase totals = $1,250.49       $1,384.3772   $1,384.38   $1,384.45   $1,384.30