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	$61.77	13.498%	$70.1077	$70.11	$70.10	$70.10
Purchase #2	$156.39	9.468%	$171.197	$171.20	$171.20	$171.20
Purchase #3	$106.54	11.602%	$118.9008	$118.90	$118.90	$118.90
Purchase #4	$137.43	9.707%	$150.7703	$150.77	$150.75	$150.80
Purchase #5	$129.68	7.618%	$139.559	$139.56	$139.55	$139.60
Purchase #6	$53.60	10.648%	$59.3073	$59.31	$59.30	$59.30
Purchase #7	$220.38	9.216%	$240.6902	$240.69	$240.70	$240.70
7 purchase totals =	$865.79		$950.5323	$950.54	$950.50	$950.60