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 $228.91   5.287%   $241.0125   $241.01   $241.00   $241.00  
  Purchase #2 $182.93   12.167%   $205.1871   $205.19   $205.20   $205.20  
  Purchase #3 $171.94   6.306%   $182.7825   $182.78   $182.80   $182.80  
  Purchase #4 $193.91   4.562%   $202.7562   $202.76   $202.75   $202.80  
  Purchase #5 $10.91   11.692%   $12.1856   $12.19   $12.20   $12.20  
  Purchase #6 $188.40   10.377%   $207.9503   $207.95   $207.95   $208.00  
  Purchase #7 $210.52   12.738%   $237.336   $237.34   $237.35   $237.30  
  7 purchase totals = $1,187.52       $1,289.2102   $1,289.22   $1,289.25   $1,289.30