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	$19.66	5.865%	$20.8131	$20.81	$20.80	$20.80
Purchase #2	$81.61	13.389%	$92.5368	$92.54	$92.55	$92.50
Purchase #3	$83.90	10.716%	$92.8907	$92.89	$92.90	$92.90
Purchase #4	$119.97	8.132%	$129.726	$129.73	$129.75	$129.70
Purchase #5	$36.89	13.339%	$41.8108	$41.81	$41.80	$41.80
Purchase #6	$76.78	6.526%	$81.7907	$81.79	$81.80	$81.80
Purchase #7	$84.57	7.296%	$90.7402	$90.74	$90.75	$90.70
7 purchase totals =	$503.38		$550.3083	$550.31	$550.35	$550.20