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	$120.31	9.642%	$131.9103	$131.91	$131.90	$131.90
Purchase #2	$221.82	13.428%	$251.606	$251.61	$251.60	$251.60
Purchase #3	$83.41	13.138%	$94.3684	$94.37	$94.35	$94.40
Purchase #4	$142.72	12.779%	$160.9582	$160.96	$160.95	$161.00
Purchase #5	$52.77	9.519%	$57.7932	$57.79	$57.80	$57.80
Purchase #6	$151.27	11.238%	$168.2697	$168.27	$168.25	$168.30
Purchase #7	$132.42	11.290%	$147.3702	$147.37	$147.35	$147.40
7 purchase totals =	$904.72		$1,012.2760	$1,012.28	$1,012.20	$1,012.40