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 $87.36   10.286%   $96.3458   $96.35   $96.35   $96.30  
  Purchase #2 $24.46   7.706%   $26.3449   $26.34   $26.35   $26.30  
  Purchase #3 $127.39   5.804%   $134.7837   $134.78   $134.80   $134.80  
  Purchase #4 $218.58   9.685%   $239.7495   $239.75   $239.75   $239.70  
  Purchase #5 $144.79   11.815%   $161.8969   $161.90   $161.90   $161.90  
  Purchase #6 $24.88   6.642%   $26.5325   $26.53   $26.55   $26.50  
  Purchase #7 $34.33   3.811%   $35.6383   $35.64   $35.65   $35.60  
  7 purchase totals = $661.79       $721.2916   $721.29   $721.35   $721.10