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	$33.88	10.190%	$37.3324	$37.33	$37.35	$37.30
Purchase #2	$45.94	13.697%	$52.2324	$52.23	$52.25	$52.20
Purchase #3	$92.34	10.770%	$102.285	$102.29	$102.30	$102.30
Purchase #4	$201.68	10.194%	$222.2393	$222.24	$222.25	$222.20
Purchase #5	$168.80	4.194%	$175.8795	$175.88	$175.90	$175.90
Purchase #6	$78.53	10.809%	$87.0183	$87.02	$87.00	$87.00
Purchase #7	$144.79	4.784%	$151.7168	$151.72	$151.70	$151.70
7 purchase totals =	$765.96		$828.7037	$828.71	$828.75	$828.60