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	$84.86	4.777%	$88.9138	$88.91	$88.90	$88.90
Purchase #2	$219.34	11.733%	$245.0752	$245.08	$245.10	$245.10
Purchase #3	$81.52	12.154%	$91.4279	$91.43	$91.45	$91.40
Purchase #4	$93.55	7.455%	$100.5242	$100.52	$100.50	$100.50
Purchase #5	$101.90	11.216%	$113.3291	$113.33	$113.35	$113.30
Purchase #6	$223.66	12.277%	$251.1187	$251.12	$251.10	$251.10
Purchase #7	$151.43	10.504%	$167.3362	$167.34	$167.35	$167.30
7 purchase totals =	$956.26		$1,057.7251	$1,057.73	$1,057.75	$1,057.60