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	$221.40	11.245%	$246.2964	$246.30	$246.30	$246.30
Purchase #2	$54.32	10.134%	$59.8248	$59.82	$59.80	$59.80
Purchase #3	$122.70	8.662%	$133.3283	$133.33	$133.35	$133.30
Purchase #4	$222.30	10.472%	$245.5793	$245.58	$245.60	$245.60
Purchase #5	$230.41	5.480%	$243.0365	$243.04	$243.05	$243.00
Purchase #6	$37.95	11.214%	$42.2057	$42.21	$42.20	$42.20
Purchase #7	$7.89	5.617%	$8.3332	$8.33	$8.35	$8.30
7 purchase totals =	$896.97		$978.6042	$978.61	$978.65	$978.50