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	$191.58	6.413%	$203.866	$203.87	$203.85	$203.90
Purchase #2	$80.73	3.510%	$83.5636	$83.56	$83.55	$83.60
Purchase #3	$6.28	9.699%	$6.8891	$6.89	$6.90	$6.90
Purchase #4	$243.48	4.137%	$253.5528	$253.55	$253.55	$253.60
Purchase #5	$133.59	12.368%	$150.1124	$150.11	$150.10	$150.10
Purchase #6	$138.46	5.474%	$146.0393	$146.04	$146.05	$146.00
Purchase #7	$59.38	11.676%	$66.3132	$66.31	$66.30	$66.30
7 purchase totals =	$853.50		$910.3364	$910.33	$910.30	$910.40