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 $111.69   12.777%   $125.9606   $125.96   $125.95   $126.00  
  Purchase #2 $193.81   12.360%   $217.7649   $217.76   $217.75   $217.80  
  Purchase #3 $189.94   6.487%   $202.2614   $202.26   $202.25   $202.30  
  Purchase #4 $45.72   4.755%   $47.894   $47.89   $47.90   $47.90  
  Purchase #5 $171.62   12.334%   $192.7876   $192.79   $192.80   $192.80  
  Purchase #6 $129.65   10.554%   $143.3333   $143.33   $143.35   $143.30  
  Purchase #7 $232.54   12.112%   $260.7052   $260.71   $260.70   $260.70  
  7 purchase totals = $1,074.97       $1,190.7070   $1,190.70   $1,190.70   $1,190.80