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 $111.42   6.123%   $118.2422   $118.24   $118.25   $118.20  
  Purchase #2 $209.95   3.294%   $216.8658   $216.87   $216.85   $216.90  
  Purchase #3 $30.86   6.756%   $32.9449   $32.94   $32.95   $32.90  
  Purchase #4 $205.86   5.639%   $217.4684   $217.47   $217.45   $217.50  
  Purchase #5 $214.48   9.319%   $234.4674   $234.47   $234.45   $234.50  
  Purchase #6 $189.96   12.276%   $213.2795   $213.28   $213.30   $213.30  
  Purchase #7 $198.49   6.521%   $211.4335   $211.43   $211.45   $211.40  
  7 purchase totals = $1,161.02       $1,244.7017   $1,244.70   $1,244.70   $1,244.70