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 $59.46   5.470%   $62.7125   $62.71   $62.70   $62.70  
  Purchase #2 $212.56   7.752%   $229.0377   $229.04   $229.05   $229.00  
  Purchase #3 $116.75   7.683%   $125.7199   $125.72   $125.70   $125.70  
  Purchase #4 $233.31   10.188%   $257.0796   $257.08   $257.10   $257.10  
  Purchase #5 $199.29   4.799%   $208.8539   $208.85   $208.85   $208.90  
  Purchase #6 $65.63   12.376%   $73.7524   $73.75   $73.75   $73.80  
  Purchase #7 $33.71   5.449%   $35.5469   $35.55   $35.55   $35.50  
  7 purchase totals = $920.71       $992.7029   $992.70   $992.70   $992.70