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 $240.83   5.468%   $253.9986   $254.00   $254.00   $254.00  
  Purchase #2 $184.49   10.492%   $203.8467   $203.85   $203.85   $203.80  
  Purchase #3 $212.49   13.853%   $241.9262   $241.93   $241.95   $241.90  
  Purchase #4 $129.53   6.461%   $137.8989   $137.90   $137.90   $137.90  
  Purchase #5 $25.89   11.688%   $28.916   $28.92   $28.90   $28.90  
  Purchase #6 $180.77   5.714%   $191.0992   $191.10   $191.10   $191.10  
  Purchase #7 $146.58   3.441%   $151.6238   $151.62   $151.60   $151.60  
  7 purchase totals = $1,120.58       $1,209.3094   $1,209.32   $1,209.30   $1,209.20