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 $211.69   9.688%   $232.1985   $232.20   $232.20   $232.20  
  Purchase #2 $188.54   11.196%   $209.6489   $209.65   $209.65   $209.60  
  Purchase #3 $141.30   5.872%   $149.5971   $149.60   $149.60   $149.60  
  Purchase #4 $156.35   11.146%   $173.7768   $173.78   $173.80   $173.80  
  Purchase #5 $21.86   10.491%   $24.1533   $24.15   $24.15   $24.20  
  Purchase #6 $24.64   6.113%   $26.1462   $26.15   $26.15   $26.10  
  Purchase #7 $147.79   4.407%   $154.3031   $154.30   $154.30   $154.30  
  7 purchase totals = $892.17       $969.8239   $969.83   $969.85   $969.80