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	$171.57	10.512%	$189.6054	$189.61	$189.60	$189.60
Purchase #2	$90.40	10.274%	$99.6877	$99.69	$99.70	$99.70
Purchase #3	$135.91	6.413%	$144.6259	$144.63	$144.65	$144.60
Purchase #4	$67.76	5.592%	$71.5491	$71.55	$71.55	$71.50
Purchase #5	$47.90	5.573%	$50.5695	$50.57	$50.55	$50.60
Purchase #6	$43.80	3.550%	$45.3549	$45.35	$45.35	$45.40
Purchase #7	$33.56	10.726%	$37.1596	$37.16	$37.15	$37.20
7 purchase totals =	$590.90		$638.5521	$638.56	$638.55	$638.60