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	$168.75	12.191%	$189.3223	$189.32	$189.30	$189.30
Purchase #2	$45.31	9.344%	$49.5438	$49.54	$49.55	$49.50
Purchase #3	$172.25	13.275%	$195.1162	$195.12	$195.10	$195.10
Purchase #4	$209.90	12.350%	$235.8227	$235.82	$235.80	$235.80
Purchase #5	$227.72	8.199%	$246.3908	$246.39	$246.40	$246.40
Purchase #6	$114.73	7.548%	$123.3898	$123.39	$123.40	$123.40
Purchase #7	$60.88	7.590%	$65.5008	$65.50	$65.50	$65.50
7 purchase totals =	$999.54		$1,105.0864	$1,105.08	$1,105.05	$1,105.00