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	$248.79	6.289%	$264.4364	$264.44	$264.45	$264.40
Purchase #2	$195.39	13.862%	$222.475	$222.48	$222.50	$222.50
Purchase #3	$157.96	3.147%	$162.931	$162.93	$162.95	$162.90
Purchase #4	$158.89	7.610%	$170.9815	$170.98	$171.00	$171.00
Purchase #5	$40.90	11.166%	$45.4669	$45.47	$45.45	$45.50
Purchase #6	$185.51	11.263%	$206.404	$206.40	$206.40	$206.40
Purchase #7	$47.57	4.434%	$49.6793	$49.68	$49.70	$49.70
7 purchase totals =	$1,035.01		$1,122.3741	$1,122.38	$1,122.45	$1,122.40