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	$35.33	7.334%	$37.9211	$37.92	$37.90	$37.90
Purchase #2	$221.34	11.810%	$247.4803	$247.48	$247.50	$247.50
Purchase #3	$61.76	11.496%	$68.8599	$68.86	$68.85	$68.90
Purchase #4	$151.73	4.285%	$158.2316	$158.23	$158.25	$158.20
Purchase #5	$101.46	11.148%	$112.7708	$112.77	$112.75	$112.80
Purchase #6	$22.75	12.636%	$25.6247	$25.62	$25.60	$25.60
Purchase #7	$206.81	7.531%	$222.3849	$222.38	$222.40	$222.40
7 purchase totals =	$801.18		$873.2733	$873.26	$873.25	$873.30