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	$80.29	13.464%	$91.1002	$91.10	$91.10	$91.10
Purchase #2	$197.31	5.544%	$208.2489	$208.25	$208.25	$208.20
Purchase #3	$221.27	10.243%	$243.9347	$243.93	$243.95	$243.90
Purchase #4	$81.96	10.591%	$90.6404	$90.64	$90.65	$90.60
Purchase #5	$137.88	9.313%	$150.7208	$150.72	$150.70	$150.70
Purchase #6	$35.91	12.232%	$40.3025	$40.30	$40.30	$40.30
Purchase #7	$20.87	8.153%	$22.5715	$22.57	$22.55	$22.60
7 purchase totals =	$775.49		$847.5190	$847.51	$847.50	$847.40