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	$147.78	12.639%	$166.4579	$166.46	$166.45	$166.50
Purchase #2	$179.26	6.854%	$191.5465	$191.55	$191.55	$191.50
Purchase #3	$177.38	7.590%	$190.8431	$190.84	$190.85	$190.80
Purchase #4	$71.39	11.686%	$79.7326	$79.73	$79.75	$79.70
Purchase #5	$141.81	6.352%	$150.8178	$150.82	$150.80	$150.80
Purchase #6	$61.59	5.729%	$65.1185	$65.12	$65.10	$65.10
Purchase #7	$27.96	6.407%	$29.7514	$29.75	$29.75	$29.80
7 purchase totals =	$807.17		$874.2678	$874.27	$874.25	$874.20