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	$82.39	6.540%	$87.7783	$87.78	$87.80	$87.80
Purchase #2	$62.57	13.773%	$71.1878	$71.19	$71.20	$71.20
Purchase #3	$37.67	11.542%	$42.0179	$42.02	$42.00	$42.00
Purchase #4	$94.71	4.830%	$99.2845	$99.28	$99.30	$99.30
Purchase #5	$83.25	13.204%	$94.2423	$94.24	$94.25	$94.20
Purchase #6	$113.53	9.688%	$124.5288	$124.53	$124.55	$124.50
Purchase #7	$139.86	5.383%	$147.3887	$147.39	$147.40	$147.40
7 purchase totals =	$613.98		$666.4283	$666.43	$666.50	$666.40