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	$157.63	13.344%	$178.6641	$178.66	$178.65	$178.70
Purchase #2	$178.37	11.790%	$199.3998	$199.40	$199.40	$199.40
Purchase #3	$6.86	10.412%	$7.5743	$7.57	$7.55	$7.60
Purchase #4	$120.35	8.110%	$130.1104	$130.11	$130.10	$130.10
Purchase #5	$18.46	10.179%	$20.339	$20.34	$20.35	$20.30
Purchase #6	$67.78	11.140%	$75.3307	$75.33	$75.35	$75.30
Purchase #7	$82.80	7.698%	$89.1739	$89.17	$89.15	$89.20
7 purchase totals =	$632.25		$700.5922	$700.58	$700.55	$700.60