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	$31.29	13.239%	$35.4325	$35.43	$35.45	$35.40
Purchase #2	$230.49	7.363%	$247.461	$247.46	$247.45	$247.50
Purchase #3	$69.98	11.870%	$78.2866	$78.29	$78.30	$78.30
Purchase #4	$101.77	7.659%	$109.5646	$109.56	$109.55	$109.60
Purchase #5	$44.57	3.852%	$46.2868	$46.29	$46.30	$46.30
Purchase #6	$221.29	7.740%	$238.4178	$238.42	$238.40	$238.40
Purchase #7	$33.79	12.178%	$37.9049	$37.90	$37.90	$37.90
7 purchase totals =	$733.18		$793.3542	$793.35	$793.35	$793.40