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	$196.75	13.629%	$223.5651	$223.57	$223.55	$223.60
Purchase #2	$54.76	9.506%	$59.9655	$59.97	$59.95	$60.00
Purchase #3	$80.44	7.745%	$86.6701	$86.67	$86.65	$86.70
Purchase #4	$127.84	9.308%	$139.7393	$139.74	$139.75	$139.70
Purchase #5	$127.94	7.345%	$137.3372	$137.34	$137.35	$137.30
Purchase #6	$140.57	10.736%	$155.6616	$155.66	$155.65	$155.70
Purchase #7	$6.99	11.284%	$7.7788	$7.78	$7.80	$7.80
7 purchase totals =	$735.29		$810.7176	$810.73	$810.70	$810.80