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	$32.43	3.731%	$33.64	$33.64	$33.65	$33.60
Purchase #2	$219.89	7.306%	$235.9552	$235.96	$235.95	$236.00
Purchase #3	$139.49	7.867%	$150.4637	$150.46	$150.45	$150.50
Purchase #4	$180.32	8.785%	$196.1611	$196.16	$196.15	$196.20
Purchase #5	$195.80	11.844%	$218.9906	$218.99	$219.00	$219.00
Purchase #6	$144.64	4.599%	$151.292	$151.29	$151.30	$151.30
Purchase #7	$93.52	12.374%	$105.0922	$105.09	$105.10	$105.10
7 purchase totals =	$1,006.09		$1,091.5948	$1,091.59	$1,091.60	$1,091.70