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	$6.59	6.408%	$7.0123	$7.01	$7.00	$7.00
Purchase #2	$35.51	9.172%	$38.767	$38.77	$38.75	$38.80
Purchase #3	$135.35	12.397%	$152.1293	$152.13	$152.15	$152.10
Purchase #4	$139.89	12.126%	$156.8531	$156.85	$156.85	$156.90
Purchase #5	$142.51	4.784%	$149.3277	$149.33	$149.35	$149.30
Purchase #6	$37.95	11.437%	$42.2903	$42.29	$42.30	$42.30
Purchase #7	$244.85	12.283%	$274.9249	$274.92	$274.90	$274.90
7 purchase totals =	$742.65		$821.3046	$821.30	$821.30	$821.30