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 $111.25   11.852%   $124.4354   $124.44   $124.45   $124.40  
  Purchase #2 $151.53   5.353%   $159.6414   $159.64   $159.65   $159.60  
  Purchase #3 $155.99   11.114%   $173.3267   $173.33   $173.35   $173.30  
  Purchase #4 $45.74   7.149%   $49.01   $49.01   $49.00   $49.00  
  Purchase #5 $173.40   6.440%   $184.567   $184.57   $184.55   $184.60  
  Purchase #6 $16.95   7.610%   $18.2399   $18.24   $18.25   $18.20  
  Purchase #7 $81.71   13.773%   $92.9639   $92.96   $92.95   $93.00  
  7 purchase totals = $736.57       $802.1843   $802.19   $802.20   $802.10