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	$122.30	3.755%	$126.8924	$126.89	$126.90	$126.90
Purchase #2	$209.90	12.374%	$235.873	$235.87	$235.85	$235.90
Purchase #3	$160.94	10.799%	$178.3199	$178.32	$178.30	$178.30
Purchase #4	$78.38	8.648%	$85.1583	$85.16	$85.15	$85.20
Purchase #5	$96.26	4.577%	$100.6658	$100.67	$100.65	$100.70
Purchase #6	$131.94	3.696%	$136.8165	$136.82	$136.80	$136.80
Purchase #7	$241.65	10.828%	$267.8159	$267.82	$267.80	$267.80
7 purchase totals =	$1,041.37		$1,131.5418	$1,131.55	$1,131.45	$1,131.60