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 $218.41   7.414%   $234.6029   $234.60   $234.60   $234.60  
  Purchase #2 $10.29   12.737%   $11.6006   $11.60   $11.60   $11.60  
  Purchase #3 $227.64   5.548%   $240.2695   $240.27   $240.25   $240.30  
  Purchase #4 $184.42   4.681%   $193.0527   $193.05   $193.05   $193.10  
  Purchase #5 $126.36   5.819%   $133.7129   $133.71   $133.70   $133.70  
  Purchase #6 $166.75   8.448%   $180.837   $180.84   $180.85   $180.80  
  Purchase #7 $120.32   4.872%   $126.182   $126.18   $126.20   $126.20  
  7 purchase totals = $1,054.19       $1,120.2576   $1,120.25   $1,120.25   $1,120.30