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	$19.25	5.337%	$20.2774	$20.28	$20.30	$20.30
Purchase #2	$39.33	10.777%	$43.5686	$43.57	$43.55	$43.60
Purchase #3	$119.71	7.542%	$128.7385	$128.74	$128.75	$128.70
Purchase #4	$171.90	9.840%	$188.815	$188.82	$188.80	$188.80
Purchase #5	$212.45	4.407%	$221.8127	$221.81	$221.80	$221.80
Purchase #6	$69.31	11.764%	$77.4636	$77.46	$77.45	$77.50
Purchase #7	$141.66	8.731%	$154.0283	$154.03	$154.05	$154.00
7 purchase totals =	$773.61		$834.7041	$834.71	$834.70	$834.70