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 $179.90   4.595%   $188.1664   $188.17   $188.15   $188.20  
  Purchase #2 $160.69   10.840%   $178.1088   $178.11   $178.10   $178.10  
  Purchase #3 $110.25   7.105%   $118.0833   $118.08   $118.10   $118.10  
  Purchase #4 $62.27   9.830%   $68.3911   $68.39   $68.40   $68.40  
  Purchase #5 $103.39   5.412%   $108.9855   $108.99   $109.00   $109.00  
  Purchase #6 $219.65   9.848%   $241.2811   $241.28   $241.30   $241.30  
  Purchase #7 $155.82   10.454%   $172.1094   $172.11   $172.10   $172.10  
  7 purchase totals = $991.97       $1,075.1256   $1,075.13   $1,075.15   $1,075.20