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	$154.91	6.798%	$165.4408	$165.44	$165.45	$165.40
Purchase #2	$201.30	10.696%	$222.831	$222.83	$222.85	$222.80
Purchase #3	$212.34	13.582%	$241.18	$241.18	$241.20	$241.20
Purchase #4	$90.37	7.459%	$97.1107	$97.11	$97.10	$97.10
Purchase #5	$124.39	3.327%	$128.5285	$128.53	$128.55	$128.50
Purchase #6	$54.85	4.144%	$57.123	$57.12	$57.10	$57.10
Purchase #7	$57.63	11.330%	$64.1595	$64.16	$64.15	$64.20
7 purchase totals =	$895.79		$976.3735	$976.37	$976.40	$976.30