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	$50.77	3.313%	$52.452	$52.45	$52.45	$52.50
Purchase #2	$149.56	11.320%	$166.4902	$166.49	$166.50	$166.50
Purchase #3	$142.38	9.322%	$155.6527	$155.65	$155.65	$155.70
Purchase #4	$209.47	9.579%	$229.5351	$229.54	$229.55	$229.50
Purchase #5	$89.46	10.149%	$98.5393	$98.54	$98.55	$98.50
Purchase #6	$55.38	6.531%	$58.9969	$59.00	$59.00	$59.00
Purchase #7	$18.66	12.329%	$20.9606	$20.96	$20.95	$21.00
7 purchase totals =	$715.68		$782.6268	$782.63	$782.65	$782.70