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	$73.63	3.802%	$76.4294	$76.43	$76.45	$76.40
Purchase #2	$124.48	12.396%	$139.9105	$139.91	$139.90	$139.90
Purchase #3	$123.94	10.494%	$136.9463	$136.95	$136.95	$136.90
Purchase #4	$145.89	6.774%	$155.7726	$155.77	$155.75	$155.80
Purchase #5	$53.93	10.855%	$59.7841	$59.78	$59.80	$59.80
Purchase #6	$177.49	8.118%	$191.8986	$191.90	$191.90	$191.90
Purchase #7	$66.57	8.163%	$72.0041	$72.00	$72.00	$72.00
7 purchase totals =	$765.93		$832.7456	$832.74	$832.75	$832.70