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	$141.47	3.763%	$146.7935	$146.79	$146.80	$146.80
Purchase #2	$179.91	13.844%	$204.8167	$204.82	$204.80	$204.80
Purchase #3	$143.71	11.397%	$160.0886	$160.09	$160.10	$160.10
Purchase #4	$82.29	3.546%	$85.208	$85.21	$85.20	$85.20
Purchase #5	$6.94	13.643%	$7.8868	$7.89	$7.90	$7.90
Purchase #6	$65.63	11.644%	$73.272	$73.27	$73.25	$73.30
Purchase #7	$149.93	4.507%	$156.6873	$156.69	$156.70	$156.70
7 purchase totals =	$769.88		$834.7529	$834.76	$834.75	$834.80