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 $187.93   12.770%   $211.9287   $211.93   $211.95   $211.90  
  Purchase #2 $161.81   10.459%   $178.7337   $178.73   $178.75   $178.70  
  Purchase #3 $68.99   9.332%   $75.4281   $75.43   $75.45   $75.40  
  Purchase #4 $26.66   9.372%   $29.1586   $29.16   $29.15   $29.20  
  Purchase #5 $211.62   6.180%   $224.6981   $224.70   $224.70   $224.70  
  Purchase #6 $111.59   13.479%   $126.6312   $126.63   $126.65   $126.60  
  Purchase #7 $195.73   7.670%   $210.7425   $210.74   $210.75   $210.70  
  7 purchase totals = $964.33       $1,057.3209   $1,057.32   $1,057.40   $1,057.20