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	$98.61	7.367%	$105.8746	$105.87	$105.85	$105.90
Purchase #2	$117.99	5.754%	$124.7791	$124.78	$124.80	$124.80
Purchase #3	$28.64	6.711%	$30.562	$30.56	$30.55	$30.60
Purchase #4	$30.52	4.140%	$31.7835	$31.78	$31.80	$31.80
Purchase #5	$83.27	7.761%	$89.7326	$89.73	$89.75	$89.70
Purchase #6	$184.34	11.722%	$205.9483	$205.95	$205.95	$205.90
Purchase #7	$64.86	10.753%	$71.8344	$71.83	$71.85	$71.80
7 purchase totals =	$608.23		$660.5145	$660.50	$660.55	$660.50