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	$214.74	4.261%	$223.8901	$223.89	$223.90	$223.90
Purchase #2	$63.33	7.838%	$68.2938	$68.29	$68.30	$68.30
Purchase #3	$73.98	10.215%	$81.5371	$81.54	$81.55	$81.50
Purchase #4	$40.85	6.230%	$43.395	$43.40	$43.40	$43.40
Purchase #5	$243.72	12.510%	$274.2094	$274.21	$274.20	$274.20
Purchase #6	$39.26	8.418%	$42.5649	$42.56	$42.55	$42.60
Purchase #7	$130.36	9.285%	$142.4639	$142.46	$142.45	$142.50
7 purchase totals =	$806.24		$876.3542	$876.35	$876.35	$876.40