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	$210.61	12.358%	$236.6372	$236.64	$236.65	$236.60
Purchase #2	$131.73	11.258%	$146.5602	$146.56	$146.55	$146.60
Purchase #3	$24.75	4.142%	$25.7751	$25.78	$25.80	$25.80
Purchase #4	$81.58	10.214%	$89.9126	$89.91	$89.90	$89.90
Purchase #5	$248.34	8.144%	$268.5648	$268.56	$268.55	$268.60
Purchase #6	$100.65	10.819%	$111.5393	$111.54	$111.55	$111.50
Purchase #7	$88.50	10.201%	$97.5279	$97.53	$97.55	$97.50
7 purchase totals =	$886.16		$976.5171	$976.52	$976.55	$976.50