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 $173.79   13.725%   $197.6427   $197.64   $197.65   $197.60  
  Purchase #2 $117.95   6.832%   $126.0083   $126.01   $126.00   $126.00  
  Purchase #3 $10.68   4.776%   $11.1901   $11.19   $11.20   $11.20  
  Purchase #4 $30.26   13.135%   $34.2347   $34.23   $34.25   $34.20  
  Purchase #5 $202.26   3.821%   $209.9884   $209.99   $210.00   $210.00  
  Purchase #6 $171.84   13.692%   $195.3683   $195.37   $195.35   $195.40  
  Purchase #7 $192.95   12.276%   $216.6365   $216.64   $216.65   $216.60  
  7 purchase totals = $899.73       $991.0690   $991.07   $991.10   $991.00