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	$132.34	3.735%	$137.2829	$137.28	$137.30	$137.30
Purchase #2	$246.62	11.715%	$275.5115	$275.51	$275.50	$275.50
Purchase #3	$168.48	9.435%	$184.3761	$184.38	$184.40	$184.40
Purchase #4	$59.27	9.325%	$64.7969	$64.80	$64.80	$64.80
Purchase #5	$17.41	9.215%	$19.0143	$19.01	$19.00	$19.00
Purchase #6	$242.98	11.561%	$271.0709	$271.07	$271.05	$271.10
Purchase #7	$84.29	4.851%	$88.3789	$88.38	$88.40	$88.40
7 purchase totals =	$951.39		$1,040.4315	$1,040.43	$1,040.45	$1,040.50