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 $91.58   11.412%   $102.0311   $102.03   $102.05   $102.00  
  Purchase #2 $117.63   9.293%   $128.5614   $128.56   $128.55   $128.60  
  Purchase #3 $164.98   4.522%   $172.4404   $172.44   $172.45   $172.40  
  Purchase #4 $198.40   5.613%   $209.5362   $209.54   $209.55   $209.50  
  Purchase #5 $224.72   6.133%   $238.5021   $238.50   $238.50   $238.50  
  Purchase #6 $21.43   13.109%   $24.2393   $24.24   $24.25   $24.20  
  Purchase #7 $103.32   7.311%   $110.8737   $110.87   $110.85   $110.90  
  7 purchase totals = $922.06       $986.1842   $986.18   $986.20   $986.10