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	$209.87	6.205%	$222.8924	$222.89	$222.90	$222.90
Purchase #2	$100.74	12.578%	$113.4111	$113.41	$113.40	$113.40
Purchase #3	$9.73	5.303%	$10.246	$10.25	$10.25	$10.20
Purchase #4	$132.35	10.460%	$146.1938	$146.19	$146.20	$146.20
Purchase #5	$243.26	11.203%	$270.5124	$270.51	$270.50	$270.50
Purchase #6	$131.38	7.708%	$141.5068	$141.51	$141.50	$141.50
Purchase #7	$180.94	4.144%	$188.4382	$188.44	$188.45	$188.40
7 purchase totals =	$1,008.27		$1,093.2007	$1,093.20	$1,093.20	$1,093.10