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 $250.50   4.199%   $261.0185   $261.02   $261.00   $261.00  
  Purchase #2 $54.76   9.117%   $59.7525   $59.75   $59.75   $59.80  
  Purchase #3 $167.35   11.171%   $186.0447   $186.04   $186.05   $186.00  
  Purchase #4 $204.80   7.135%   $219.4125   $219.41   $219.40   $219.40  
  Purchase #5 $179.74   13.718%   $204.3967   $204.40   $204.40   $204.40  
  Purchase #6 $62.76   8.217%   $67.917   $67.92   $67.90   $67.90  
  Purchase #7 $49.36   10.815%   $54.6983   $54.70   $54.70   $54.70  
  7 purchase totals = $969.27       $1,053.2402   $1,053.24   $1,053.20   $1,053.20