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	$81.48	12.189%	$91.4116	$91.41	$91.40	$91.40
Purchase #2	$247.58	6.681%	$264.1208	$264.12	$264.10	$264.10
Purchase #3	$180.67	6.507%	$192.4262	$192.43	$192.45	$192.40
Purchase #4	$204.96	13.799%	$233.2424	$233.24	$233.25	$233.20
Purchase #5	$206.26	8.102%	$222.9712	$222.97	$222.95	$223.00
Purchase #6	$82.30	6.756%	$87.8602	$87.86	$87.85	$87.90
Purchase #7	$57.61	3.309%	$59.5163	$59.52	$59.50	$59.50
7 purchase totals =	$1,060.86		$1,151.5487	$1,151.55	$1,151.50	$1,151.50