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	$233.30	8.530%	$253.2005	$253.20	$253.20	$253.20
Purchase #2	$62.68	12.278%	$70.3759	$70.38	$70.40	$70.40
Purchase #3	$171.42	9.576%	$187.8352	$187.84	$187.85	$187.80
Purchase #4	$109.86	8.161%	$118.8257	$118.83	$118.85	$118.80
Purchase #5	$185.45	6.717%	$197.9067	$197.91	$197.90	$197.90
Purchase #6	$33.31	13.151%	$37.6906	$37.69	$37.70	$37.70
Purchase #7	$128.70	7.132%	$137.8789	$137.88	$137.90	$137.90
7 purchase totals =	$924.72		$1,003.7135	$1,003.73	$1,003.80	$1,003.70