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	$119.76	9.731%	$131.4138	$131.41	$131.40	$131.40
Purchase #2	$60.40	13.372%	$68.4767	$68.48	$68.50	$68.50
Purchase #3	$14.35	7.526%	$15.43	$15.43	$15.45	$15.40
Purchase #4	$82.51	5.639%	$87.1627	$87.16	$87.15	$87.20
Purchase #5	$99.93	6.621%	$106.5464	$106.55	$106.55	$106.50
Purchase #6	$145.39	7.735%	$156.6359	$156.64	$156.65	$156.60
Purchase #7	$81.57	9.484%	$89.3061	$89.31	$89.30	$89.30
7 purchase totals =	$603.91		$654.9716	$654.98	$655.00	$654.90