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	$157.75	9.574%	$172.853	$172.85	$172.85	$172.90
Purchase #2	$139.84	12.673%	$157.5619	$157.56	$157.55	$157.60
Purchase #3	$28.54	9.567%	$31.2704	$31.27	$31.25	$31.30
Purchase #4	$79.98	10.698%	$88.5363	$88.54	$88.55	$88.50
Purchase #5	$28.50	9.317%	$31.1553	$31.16	$31.15	$31.20
Purchase #6	$211.33	3.788%	$219.3352	$219.34	$219.35	$219.30
Purchase #7	$125.94	3.406%	$130.2295	$130.23	$130.25	$130.20
7 purchase totals =	$771.88		$830.9416	$830.95	$830.95	$831.00