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 $93.60   13.205%   $105.9599   $105.96   $105.95   $106.00  
  Purchase #2 $67.78   9.278%   $74.0686   $74.07   $74.05   $74.10  
  Purchase #3 $118.65   13.571%   $134.752   $134.75   $134.75   $134.80  
  Purchase #4 $183.64   11.497%   $204.7531   $204.75   $204.75   $204.80  
  Purchase #5 $164.66   6.405%   $175.2065   $175.21   $175.20   $175.20  
  Purchase #6 $133.73   11.415%   $148.9953   $149.00   $149.00   $149.00  
  Purchase #7 $156.61   4.276%   $163.3066   $163.31   $163.30   $163.30  
  7 purchase totals = $918.67       $1,007.0420   $1,007.05   $1,007.00   $1,007.20