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 $112.34   5.596%   $118.6265   $118.63   $118.65   $118.60  
  Purchase #2 $247.63   8.847%   $269.5378   $269.54   $269.55   $269.50  
  Purchase #3 $84.26   3.124%   $86.8923   $86.89   $86.90   $86.90  
  Purchase #4 $146.31   6.478%   $155.788   $155.79   $155.80   $155.80  
  Purchase #5 $128.89   4.216%   $134.324   $134.32   $134.30   $134.30  
  Purchase #6 $232.40   9.553%   $254.6012   $254.60   $254.60   $254.60  
  Purchase #7 $223.40   9.254%   $244.0734   $244.07   $244.05   $244.10  
  7 purchase totals = $1,175.23       $1,263.8432   $1,263.84   $1,263.85   $1,263.80