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	$226.25	12.850%	$255.3231	$255.32	$255.30	$255.30
Purchase #2	$84.89	3.205%	$87.6107	$87.61	$87.60	$87.60
Purchase #3	$133.26	12.681%	$150.1587	$150.16	$150.15	$150.20
Purchase #4	$248.33	5.311%	$261.5188	$261.52	$261.50	$261.50
Purchase #5	$53.28	8.751%	$57.9425	$57.94	$57.95	$57.90
Purchase #6	$61.38	12.653%	$69.1464	$69.15	$69.15	$69.10
Purchase #7	$128.77	8.636%	$139.8906	$139.89	$139.90	$139.90
7 purchase totals =	$936.16		$1,021.5908	$1,021.59	$1,021.55	$1,021.50