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	$5.74	7.274%	$6.1575	$6.16	$6.15	$6.20
Purchase #2	$242.67	4.635%	$253.9178	$253.92	$253.90	$253.90
Purchase #3	$222.73	10.256%	$245.5732	$245.57	$245.55	$245.60
Purchase #4	$75.87	8.761%	$82.517	$82.52	$82.50	$82.50
Purchase #5	$225.76	7.244%	$242.1141	$242.11	$242.10	$242.10
Purchase #6	$7.56	3.502%	$7.8248	$7.82	$7.80	$7.80
Purchase #7	$135.40	5.554%	$142.9201	$142.92	$142.90	$142.90
7 purchase totals =	$915.73		$981.0245	$981.02	$980.90	$981.00