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	$131.29	7.245%	$140.802	$140.80	$140.80	$140.80
Purchase #2	$141.39	6.734%	$150.9112	$150.91	$150.90	$150.90
Purchase #3	$70.80	10.571%	$78.2843	$78.28	$78.30	$78.30
Purchase #4	$168.50	10.304%	$185.8622	$185.86	$185.85	$185.90
Purchase #5	$55.44	11.371%	$61.7441	$61.74	$61.75	$61.70
Purchase #6	$204.66	8.752%	$222.5718	$222.57	$222.55	$222.60
Purchase #7	$47.76	13.749%	$54.3265	$54.33	$54.35	$54.30
7 purchase totals =	$819.84		$894.5021	$894.49	$894.50	$894.50