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	$203.62	9.215%	$222.3836	$222.38	$222.40	$222.40
Purchase #2	$99.50	11.446%	$110.8888	$110.89	$110.90	$110.90
Purchase #3	$247.44	9.530%	$271.021	$271.02	$271.00	$271.00
Purchase #4	$235.48	12.632%	$265.2258	$265.23	$265.25	$265.20
Purchase #5	$168.34	13.376%	$190.8572	$190.86	$190.85	$190.90
Purchase #6	$213.71	4.136%	$222.549	$222.55	$222.55	$222.50
Purchase #7	$196.58	4.644%	$205.7092	$205.71	$205.70	$205.70
7 purchase totals =	$1,364.67		$1,488.6346	$1,488.64	$1,488.65	$1,488.60