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	$156.59	12.102%	$175.5405	$175.54	$175.55	$175.50
Purchase #2	$217.33	10.728%	$240.6452	$240.65	$240.65	$240.60
Purchase #3	$28.48	12.723%	$32.1035	$32.10	$32.10	$32.10
Purchase #4	$248.70	4.148%	$259.0161	$259.02	$259.00	$259.00
Purchase #5	$5.45	12.108%	$6.1099	$6.11	$6.10	$6.10
Purchase #6	$125.90	13.505%	$142.9028	$142.90	$142.90	$142.90
Purchase #7	$138.37	5.846%	$146.4591	$146.46	$146.45	$146.50
7 purchase totals =	$920.82		$1,002.7771	$1,002.78	$1,002.75	$1,002.70