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	$137.80	6.802%	$147.1732	$147.17	$147.15	$147.20
Purchase #2	$249.67	3.692%	$258.8878	$258.89	$258.90	$258.90
Purchase #3	$113.40	13.566%	$128.7838	$128.78	$128.80	$128.80
Purchase #4	$85.64	6.528%	$91.2306	$91.23	$91.25	$91.20
Purchase #5	$134.43	7.657%	$144.7233	$144.72	$144.70	$144.70
Purchase #6	$48.86	12.459%	$54.9475	$54.95	$54.95	$54.90
Purchase #7	$35.51	6.715%	$37.8945	$37.89	$37.90	$37.90
7 purchase totals =	$805.31		$863.6407	$863.63	$863.65	$863.60