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 $244.96   8.237%   $265.1374   $265.14   $265.15   $265.10  
  Purchase #2 $139.62   8.838%   $151.9596   $151.96   $151.95   $152.00  
  Purchase #3 $122.26   4.579%   $127.8583   $127.86   $127.85   $127.90  
  Purchase #4 $215.56   9.735%   $236.5448   $236.54   $236.55   $236.50  
  Purchase #5 $135.35   5.610%   $142.9431   $142.94   $142.95   $142.90  
  Purchase #6 $65.58   5.607%   $69.2571   $69.26   $69.25   $69.30  
  Purchase #7 $64.45   8.445%   $69.8928   $69.89   $69.90   $69.90  
  7 purchase totals = $987.78       $1,063.5931   $1,063.59   $1,063.60   $1,063.60