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	$147.51	3.575%	$152.7835	$152.78	$152.80	$152.80
Purchase #2	$183.71	12.787%	$207.201	$207.20	$207.20	$207.20
Purchase #3	$56.66	4.710%	$59.3287	$59.33	$59.35	$59.30
Purchase #4	$160.37	9.806%	$176.0959	$176.10	$176.10	$176.10
Purchase #5	$68.48	12.623%	$77.1242	$77.12	$77.10	$77.10
Purchase #6	$85.36	5.217%	$89.8132	$89.81	$89.80	$89.80
Purchase #7	$36.37	3.843%	$37.7677	$37.77	$37.75	$37.80
7 purchase totals =	$738.46		$800.1142	$800.11	$800.10	$800.10