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	$242.30	13.562%	$275.1607	$275.16	$275.15	$275.20
Purchase #2	$78.53	11.524%	$87.5798	$87.58	$87.60	$87.60
Purchase #3	$182.66	3.870%	$189.7289	$189.73	$189.75	$189.70
Purchase #4	$43.47	4.836%	$45.5722	$45.57	$45.55	$45.60
Purchase #5	$112.70	9.721%	$123.6556	$123.66	$123.65	$123.70
Purchase #6	$105.53	5.112%	$110.9247	$110.92	$110.90	$110.90
Purchase #7	$238.41	3.726%	$247.2932	$247.29	$247.30	$247.30
7 purchase totals =	$1,003.60		$1,079.9151	$1,079.91	$1,079.90	$1,080.00