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	$242.63	11.425%	$270.3505	$270.35	$270.35	$270.40
Purchase #2	$18.86	8.618%	$20.4854	$20.49	$20.50	$20.50
Purchase #3	$197.70	12.683%	$222.7743	$222.77	$222.75	$222.80
Purchase #4	$179.75	6.471%	$191.3816	$191.38	$191.40	$191.40
Purchase #5	$91.35	13.283%	$103.484	$103.48	$103.50	$103.50
Purchase #6	$13.73	3.590%	$14.2229	$14.22	$14.20	$14.20
Purchase #7	$232.38	5.772%	$245.793	$245.79	$245.80	$245.80
7 purchase totals =	$976.40		$1,068.4917	$1,068.48	$1,068.50	$1,068.60