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	$231.29	12.682%	$260.6222	$260.62	$260.60	$260.60
Purchase #2	$36.40	11.445%	$40.566	$40.57	$40.55	$40.60
Purchase #3	$90.33	8.843%	$98.3179	$98.32	$98.30	$98.30
Purchase #4	$194.46	8.798%	$211.5686	$211.57	$211.55	$211.60
Purchase #5	$72.26	6.846%	$77.2069	$77.21	$77.20	$77.20
Purchase #6	$57.78	6.707%	$61.6553	$61.66	$61.65	$61.70
Purchase #7	$148.73	13.562%	$168.9008	$168.90	$168.90	$168.90
7 purchase totals =	$831.25		$918.8377	$918.85	$918.75	$918.90