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 $62.96   10.368%   $69.4877   $69.49   $69.50   $69.50  
  Purchase #2 $98.95   4.344%   $103.2484   $103.25   $103.25   $103.20  
  Purchase #3 $76.68   4.633%   $80.2326   $80.23   $80.25   $80.20  
  Purchase #4 $114.76   8.283%   $124.2656   $124.27   $124.25   $124.30  
  Purchase #5 $29.75   5.380%   $31.3506   $31.35   $31.35   $31.40  
  Purchase #6 $172.70   6.701%   $184.2726   $184.27   $184.25   $184.30  
  Purchase #7 $88.47   4.730%   $92.6546   $92.65   $92.65   $92.70  
  7 purchase totals = $644.27       $685.5121   $685.51   $685.50   $685.60