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 $36.81   11.496%   $41.0417   $41.04   $41.05   $41.00  
  Purchase #2 $22.45   13.840%   $25.5571   $25.56   $25.55   $25.60  
  Purchase #3 $246.94   3.726%   $256.141   $256.14   $256.15   $256.10  
  Purchase #4 $249.47   5.231%   $262.5198   $262.52   $262.50   $262.50  
  Purchase #5 $197.45   10.359%   $217.9038   $217.90   $217.90   $217.90  
  Purchase #6 $176.32   6.449%   $187.6909   $187.69   $187.70   $187.70  
  Purchase #7 $246.59   11.267%   $274.3733   $274.37   $274.35   $274.40  
  7 purchase totals = $1,176.03       $1,265.2276   $1,265.22   $1,265.20   $1,265.20