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 $181.95   8.826%   $198.0089   $198.01   $198.00   $198.00  
  Purchase #2 $118.94   13.747%   $135.2907   $135.29   $135.30   $135.30  
  Purchase #3 $55.63   10.326%   $61.3744   $61.37   $61.35   $61.40  
  Purchase #4 $12.67   9.788%   $13.9101   $13.91   $13.90   $13.90  
  Purchase #5 $54.25   12.794%   $61.1907   $61.19   $61.20   $61.20  
  Purchase #6 $214.90   9.837%   $236.0397   $236.04   $236.05   $236.00  
  Purchase #7 $218.85   11.651%   $244.3482   $244.35   $244.35   $244.30  
  7 purchase totals = $857.19       $950.1627   $950.16   $950.15   $950.10