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	$32.56	12.739%	$36.7078	$36.71	$36.70	$36.70
Purchase #2	$102.95	6.134%	$109.265	$109.27	$109.25	$109.30
Purchase #3	$213.72	11.371%	$238.0221	$238.02	$238.00	$238.00
Purchase #4	$136.39	13.874%	$155.3127	$155.31	$155.30	$155.30
Purchase #5	$216.45	11.131%	$240.543	$240.54	$240.55	$240.50
Purchase #6	$246.76	3.538%	$255.4904	$255.49	$255.50	$255.50
Purchase #7	$231.29	11.394%	$257.6432	$257.64	$257.65	$257.60
7 purchase totals =	$1,180.12		$1,292.9842	$1,292.98	$1,292.95	$1,292.90