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	$91.74	5.646%	$96.9196	$96.92	$96.90	$96.90
Purchase #2	$83.89	5.277%	$88.3169	$88.32	$88.30	$88.30
Purchase #3	$33.65	12.470%	$37.8462	$37.85	$37.85	$37.80
Purchase #4	$59.71	5.217%	$62.8251	$62.83	$62.85	$62.80
Purchase #5	$93.98	9.457%	$102.8677	$102.87	$102.85	$102.90
Purchase #6	$73.44	12.733%	$82.7911	$82.79	$82.80	$82.80
Purchase #7	$96.75	13.231%	$109.551	$109.55	$109.55	$109.60
7 purchase totals =	$533.16		$581.1176	$581.13	$581.10	$581.10