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 $44.41   13.192%   $50.2686   $50.27   $50.25   $50.30  
  Purchase #2 $226.35   4.414%   $236.3411   $236.34   $236.35   $236.30  
  Purchase #3 $216.89   12.777%   $244.602   $244.60   $244.60   $244.60  
  Purchase #4 $186.52   3.306%   $192.6864   $192.69   $192.70   $192.70  
  Purchase #5 $239.44   8.248%   $259.189   $259.19   $259.20   $259.20  
  Purchase #6 $25.68   3.222%   $26.5074   $26.51   $26.50   $26.50  
  Purchase #7 $88.67   4.481%   $92.6433   $92.64   $92.65   $92.60  
  7 purchase totals = $1,027.96       $1,102.2378   $1,102.24   $1,102.25   $1,102.20