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 $195.84   10.120%   $215.659   $215.66   $215.65   $215.70  
  Purchase #2 $242.80   5.137%   $255.2726   $255.27   $255.25   $255.30  
  Purchase #3 $208.31   13.581%   $236.6006   $236.60   $236.60   $236.60  
  Purchase #4 $48.71   3.414%   $50.373   $50.37   $50.35   $50.40  
  Purchase #5 $131.56   13.369%   $149.1483   $149.15   $149.15   $149.10  
  Purchase #6 $61.94   13.771%   $70.4698   $70.47   $70.45   $70.50  
  Purchase #7 $239.31   13.861%   $272.4808   $272.48   $272.50   $272.50  
  7 purchase totals = $1,128.47       $1,250.0041   $1,250.00   $1,249.95   $1,250.10