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	$37.96	10.556%	$41.9671	$41.97	$41.95	$42.00
Purchase #2	$197.73	13.193%	$223.8165	$223.82	$223.80	$223.80
Purchase #3	$66.40	8.799%	$72.2425	$72.24	$72.25	$72.20
Purchase #4	$41.83	10.453%	$46.2025	$46.20	$46.20	$46.20
Purchase #5	$247.88	10.287%	$273.3794	$273.38	$273.40	$273.40
Purchase #6	$169.65	12.444%	$190.7612	$190.76	$190.75	$190.80
Purchase #7	$18.89	6.440%	$20.1065	$20.11	$20.10	$20.10
7 purchase totals =	$780.34		$868.4757	$868.48	$868.45	$868.50