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	$40.53	3.661%	$42.0138	$42.01	$42.00	$42.00
Purchase #2	$166.40	9.664%	$182.4809	$182.48	$182.50	$182.50
Purchase #3	$249.48	10.488%	$275.6455	$275.65	$275.65	$275.60
Purchase #4	$71.33	8.684%	$77.5243	$77.52	$77.50	$77.50
Purchase #5	$96.62	3.147%	$99.6606	$99.66	$99.65	$99.70
Purchase #6	$112.35	5.606%	$118.6483	$118.65	$118.65	$118.60
Purchase #7	$135.39	11.363%	$150.7744	$150.77	$150.75	$150.80
7 purchase totals =	$872.10		$946.7478	$946.74	$946.70	$946.70