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	$69.37	4.742%	$72.6595	$72.66	$72.65	$72.70
Purchase #2	$40.37	6.190%	$42.8689	$42.87	$42.85	$42.90
Purchase #3	$144.56	12.460%	$162.5722	$162.57	$162.55	$162.60
Purchase #4	$244.50	12.442%	$274.9207	$274.92	$274.90	$274.90
Purchase #5	$166.82	8.386%	$180.8095	$180.81	$180.80	$180.80
Purchase #6	$199.86	10.802%	$221.4489	$221.45	$221.45	$221.40
Purchase #7	$34.69	7.414%	$37.2619	$37.26	$37.25	$37.30
7 purchase totals =	$900.17		$992.5416	$992.54	$992.45	$992.60