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	$156.81	9.387%	$171.5298	$171.53	$171.55	$171.50
Purchase #2	$182.82	5.147%	$192.2297	$192.23	$192.25	$192.20
Purchase #3	$82.35	8.613%	$89.4428	$89.44	$89.45	$89.40
Purchase #4	$126.26	10.362%	$139.3431	$139.34	$139.35	$139.30
Purchase #5	$120.72	3.450%	$124.8848	$124.88	$124.90	$124.90
Purchase #6	$149.44	7.531%	$160.6943	$160.69	$160.70	$160.70
Purchase #7	$53.53	12.740%	$60.3497	$60.35	$60.35	$60.30
7 purchase totals =	$871.93		$938.4742	$938.46	$938.55	$938.30