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	$64.31	10.667%	$71.1699	$71.17	$71.15	$71.20
Purchase #2	$225.31	7.578%	$242.384	$242.38	$242.40	$242.40
Purchase #3	$180.56	4.561%	$188.7953	$188.80	$188.80	$188.80
Purchase #4	$41.49	9.382%	$45.3826	$45.38	$45.40	$45.40
Purchase #5	$165.73	8.279%	$179.4508	$179.45	$179.45	$179.50
Purchase #6	$224.26	10.480%	$247.7624	$247.76	$247.75	$247.80
Purchase #7	$239.41	12.697%	$269.8079	$269.81	$269.80	$269.80
7 purchase totals =	$1,141.07		$1,244.7529	$1,244.75	$1,244.75	$1,244.90