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 $141.83   9.188%   $154.8613   $154.86   $154.85   $154.90  
  Purchase #2 $236.82   7.394%   $254.3305   $254.33   $254.35   $254.30  
  Purchase #3 $176.89   12.368%   $198.7678   $198.77   $198.75   $198.80  
  Purchase #4 $224.26   5.661%   $236.9554   $236.96   $236.95   $237.00  
  Purchase #5 $238.73   3.307%   $246.6248   $246.62   $246.60   $246.60  
  Purchase #6 $204.95   13.167%   $231.9358   $231.94   $231.95   $231.90  
  Purchase #7 $218.93   8.826%   $238.2528   $238.25   $238.25   $238.30  
  7 purchase totals = $1,442.41       $1,561.7284   $1,561.73   $1,561.70   $1,561.80