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	$151.88	5.202%	$159.7808	$159.78	$159.80	$159.80
Purchase #2	$90.37	12.215%	$101.4087	$101.41	$101.40	$101.40
Purchase #3	$242.54	5.498%	$255.8748	$255.87	$255.85	$255.90
Purchase #4	$250.45	5.706%	$264.7407	$264.74	$264.75	$264.70
Purchase #5	$241.49	13.571%	$274.2626	$274.26	$274.25	$274.30
Purchase #6	$212.33	12.206%	$238.247	$238.25	$238.25	$238.20
Purchase #7	$79.57	7.140%	$85.2513	$85.25	$85.25	$85.30
7 purchase totals =	$1,268.63		$1,379.5659	$1,379.56	$1,379.55	$1,379.60