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 $57.62   7.381%   $61.8729   $61.87   $61.85   $61.90  
  Purchase #2 $233.79   13.199%   $264.6479   $264.65   $264.65   $264.60  
  Purchase #3 $48.72   6.233%   $51.7567   $51.76   $51.75   $51.80  
  Purchase #4 $83.67   4.639%   $87.5515   $87.55   $87.55   $87.60  
  Purchase #5 $164.32   5.117%   $172.7283   $172.73   $172.75   $172.70  
  Purchase #6 $245.77   12.601%   $276.7395   $276.74   $276.75   $276.70  
  Purchase #7 $7.49   10.309%   $8.2621   $8.26   $8.25   $8.30  
  7 purchase totals = $841.38       $923.5589   $923.56   $923.55   $923.60