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 $243.44   6.855%   $260.1278   $260.13   $260.15   $260.10  
  Purchase #2 $189.96   9.867%   $208.7034   $208.70   $208.70   $208.70  
  Purchase #3 $15.44   5.832%   $16.3405   $16.34   $16.35   $16.30  
  Purchase #4 $64.31   7.792%   $69.321   $69.32   $69.30   $69.30  
  Purchase #5 $208.39   8.668%   $226.4532   $226.45   $226.45   $226.50  
  Purchase #6 $114.62   7.260%   $122.9414   $122.94   $122.95   $122.90  
  Purchase #7 $33.76   11.163%   $37.5286   $37.53   $37.55   $37.50  
  7 purchase totals = $869.92       $941.4159   $941.41   $941.45   $941.30