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	$216.51	3.130%	$223.2868	$223.29	$223.30	$223.30
Purchase #2	$148.56	3.223%	$153.3481	$153.35	$153.35	$153.30
Purchase #3	$7.39	3.231%	$7.6288	$7.63	$7.65	$7.60
Purchase #4	$245.57	9.461%	$268.8034	$268.80	$268.80	$268.80
Purchase #5	$37.56	8.511%	$40.7567	$40.76	$40.75	$40.80
Purchase #6	$145.50	7.157%	$155.9134	$155.91	$155.90	$155.90
Purchase #7	$150.85	11.275%	$167.8583	$167.86	$167.85	$167.90
7 purchase totals =	$951.94		$1,017.5955	$1,017.60	$1,017.60	$1,017.60