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 $16.54   13.233%   $18.7287   $18.73   $18.75   $18.70  
  Purchase #2 $229.73   6.469%   $244.5912   $244.59   $244.60   $244.60  
  Purchase #3 $144.59   11.208%   $160.7956   $160.80   $160.80   $160.80  
  Purchase #4 $86.50   5.636%   $91.3751   $91.38   $91.40   $91.40  
  Purchase #5 $237.96   4.211%   $247.9805   $247.98   $248.00   $248.00  
  Purchase #6 $162.75   7.282%   $174.6015   $174.60   $174.60   $174.60  
  Purchase #7 $118.99   5.503%   $125.538   $125.54   $125.55   $125.50  
  7 purchase totals = $997.06       $1,063.6106   $1,063.62   $1,063.70   $1,063.60