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	$45.86	12.753%	$51.7085	$51.71	$51.70	$51.70
Purchase #2	$153.98	3.419%	$159.2446	$159.24	$159.25	$159.20
Purchase #3	$159.36	6.632%	$169.9288	$169.93	$169.95	$169.90
Purchase #4	$250.78	5.495%	$264.5604	$264.56	$264.55	$264.60
Purchase #5	$29.98	9.538%	$32.8395	$32.84	$32.85	$32.80
Purchase #6	$244.26	12.588%	$275.0074	$275.01	$275.00	$275.00
Purchase #7	$203.57	11.564%	$227.1108	$227.11	$227.10	$227.10
7 purchase totals =	$1,087.79		$1,180.4000	$1,180.40	$1,180.40	$1,180.30