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	$80.67	13.190%	$91.3104	$91.31	$91.30	$91.30
Purchase #2	$77.34	10.226%	$85.2488	$85.25	$85.25	$85.20
Purchase #3	$96.44	8.482%	$104.62	$104.62	$104.60	$104.60
Purchase #4	$213.89	5.815%	$226.3277	$226.33	$226.35	$226.30
Purchase #5	$121.91	7.288%	$130.7948	$130.79	$130.80	$130.80
Purchase #6	$88.85	11.591%	$99.1486	$99.15	$99.15	$99.10
Purchase #7	$61.48	7.613%	$66.1605	$66.16	$66.15	$66.20
7 purchase totals =	$740.58		$803.6108	$803.61	$803.60	$803.50