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 $208.60   7.323%   $223.8758   $223.88   $223.90   $223.90  
  Purchase #2 $88.43   6.487%   $94.1665   $94.17   $94.15   $94.20  
  Purchase #3 $61.56   7.484%   $66.1672   $66.17   $66.15   $66.20  
  Purchase #4 $196.71   8.671%   $213.7667   $213.77   $213.75   $213.80  
  Purchase #5 $22.88   6.352%   $24.3333   $24.33   $24.35   $24.30  
  Purchase #6 $203.27   5.314%   $214.0718   $214.07   $214.05   $214.10  
  Purchase #7 $22.85   5.328%   $24.0674   $24.07   $24.05   $24.10  
  7 purchase totals = $804.30       $860.4487   $860.46   $860.40   $860.60