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	$113.88	6.316%	$121.0727	$121.07	$121.05	$121.10
Purchase #2	$165.28	4.334%	$172.4432	$172.44	$172.45	$172.40
Purchase #3	$117.25	12.205%	$131.5604	$131.56	$131.55	$131.60
Purchase #4	$127.57	11.687%	$142.4791	$142.48	$142.50	$142.50
Purchase #5	$206.89	6.309%	$219.9427	$219.94	$219.95	$219.90
Purchase #6	$194.41	9.327%	$212.5426	$212.54	$212.55	$212.50
Purchase #7	$139.29	5.112%	$146.4105	$146.41	$146.40	$146.40
7 purchase totals =	$1,064.57		$1,146.4512	$1,146.44	$1,146.45	$1,146.40