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	$38.55	11.488%	$42.9786	$42.98	$43.00	$43.00
Purchase #2	$64.84	8.704%	$70.4837	$70.48	$70.50	$70.50
Purchase #3	$197.72	5.822%	$209.2313	$209.23	$209.25	$209.20
Purchase #4	$92.62	3.141%	$95.5292	$95.53	$95.55	$95.50
Purchase #5	$45.33	5.359%	$47.7592	$47.76	$47.75	$47.80
Purchase #6	$73.61	12.485%	$82.8002	$82.80	$82.80	$82.80
Purchase #7	$78.97	5.238%	$83.1064	$83.11	$83.10	$83.10
7 purchase totals =	$591.64		$631.8886	$631.89	$631.95	$631.90