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	$92.52	5.389%	$97.5059	$97.51	$97.50	$97.50
Purchase #2	$191.66	9.514%	$209.8945	$209.89	$209.90	$209.90
Purchase #3	$133.54	13.288%	$151.2848	$151.28	$151.30	$151.30
Purchase #4	$68.86	12.306%	$77.3339	$77.33	$77.35	$77.30
Purchase #5	$66.74	8.121%	$72.16	$72.16	$72.15	$72.20
Purchase #6	$178.72	9.721%	$196.0934	$196.09	$196.10	$196.10
Purchase #7	$186.75	8.297%	$202.2446	$202.24	$202.25	$202.20
7 purchase totals =	$918.79		$1,006.5171	$1,006.50	$1,006.55	$1,006.50