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	$39.33	4.313%	$41.0263	$41.03	$41.05	$41.00
Purchase #2	$46.34	4.595%	$48.4693	$48.47	$48.45	$48.50
Purchase #3	$160.89	12.785%	$181.4598	$181.46	$181.45	$181.50
Purchase #4	$122.60	12.494%	$137.9176	$137.92	$137.90	$137.90
Purchase #5	$189.46	7.467%	$203.607	$203.61	$203.60	$203.60
Purchase #6	$35.93	6.666%	$38.3251	$38.33	$38.35	$38.30
Purchase #7	$37.31	8.300%	$40.4067	$40.41	$40.40	$40.40
7 purchase totals =	$631.86		$691.2118	$691.23	$691.20	$691.20