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 $107.51   10.218%   $118.4954   $118.50   $118.50   $118.50  
  Purchase #2 $124.36   9.864%   $136.6269   $136.63   $136.65   $136.60  
  Purchase #3 $219.71   3.651%   $227.7316   $227.73   $227.75   $227.70  
  Purchase #4 $145.34   4.250%   $151.517   $151.52   $151.50   $151.50  
  Purchase #5 $12.47   11.171%   $13.863   $13.86   $13.85   $13.90  
  Purchase #6 $226.39   3.424%   $234.1416   $234.14   $234.15   $234.10  
  Purchase #7 $133.61   6.435%   $142.2078   $142.21   $142.20   $142.20  
  7 purchase totals = $969.39       $1,024.5833   $1,024.59   $1,024.60   $1,024.50