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	$46.67	12.415%	$52.4641	$52.46	$52.45	$52.50
Purchase #2	$159.82	5.428%	$168.495	$168.50	$168.50	$168.50
Purchase #3	$211.48	8.374%	$229.1893	$229.19	$229.20	$229.20
Purchase #4	$57.48	4.146%	$59.8631	$59.86	$59.85	$59.90
Purchase #5	$79.95	3.766%	$82.9609	$82.96	$82.95	$83.00
Purchase #6	$144.83	7.656%	$155.9182	$155.92	$155.90	$155.90
Purchase #7	$189.96	6.568%	$202.4366	$202.44	$202.45	$202.40
7 purchase totals =	$890.19		$951.3272	$951.33	$951.30	$951.40