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	$231.74	10.533%	$256.1492	$256.15	$256.15	$256.10
Purchase #2	$105.92	5.600%	$111.8515	$111.85	$111.85	$111.90
Purchase #3	$123.35	6.415%	$131.2629	$131.26	$131.25	$131.30
Purchase #4	$84.67	10.463%	$93.529	$93.53	$93.55	$93.50
Purchase #5	$152.90	5.210%	$160.8661	$160.87	$160.85	$160.90
Purchase #6	$84.36	3.518%	$87.3278	$87.33	$87.35	$87.30
Purchase #7	$81.79	9.650%	$89.6827	$89.68	$89.70	$89.70
7 purchase totals =	$864.73		$930.6692	$930.67	$930.70	$930.70