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	$39.39	7.532%	$42.3569	$42.36	$42.35	$42.40
Purchase #2	$37.79	10.752%	$41.8532	$41.85	$41.85	$41.90
Purchase #3	$30.36	5.687%	$32.0866	$32.09	$32.10	$32.10
Purchase #4	$85.68	3.741%	$88.8853	$88.89	$88.90	$88.90
Purchase #5	$125.70	13.364%	$142.4985	$142.50	$142.50	$142.50
Purchase #6	$176.66	11.267%	$196.5643	$196.56	$196.55	$196.60
Purchase #7	$237.65	7.133%	$254.6016	$254.60	$254.60	$254.60
7 purchase totals =	$733.23		$798.8464	$798.85	$798.85	$799.00