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 $88.71   8.412%   $96.1723   $96.17   $96.15   $96.20  
  Purchase #2 $5.46   12.172%   $6.1246   $6.12   $6.10   $6.10  
  Purchase #3 $120.76   11.272%   $134.3721   $134.37   $134.35   $134.40  
  Purchase #4 $170.91   12.797%   $192.7814   $192.78   $192.80   $192.80  
  Purchase #5 $244.57   3.118%   $252.1957   $252.20   $252.20   $252.20  
  Purchase #6 $236.37   11.240%   $262.938   $262.94   $262.95   $262.90  
  Purchase #7 $92.47   9.763%   $101.4978   $101.50   $101.50   $101.50  
  7 purchase totals = $959.25       $1,046.0819   $1,046.08   $1,046.05   $1,046.10