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	$40.90	3.129%	$42.1798	$42.18	$42.20	$42.20
Purchase #2	$132.84	9.843%	$145.9154	$145.92	$145.90	$145.90
Purchase #3	$205.76	11.515%	$229.4533	$229.45	$229.45	$229.50
Purchase #4	$38.40	8.199%	$41.5484	$41.55	$41.55	$41.50
Purchase #5	$229.81	6.165%	$243.9778	$243.98	$244.00	$244.00
Purchase #6	$64.26	11.871%	$71.8883	$71.89	$71.90	$71.90
Purchase #7	$224.57	9.534%	$245.9805	$245.98	$246.00	$246.00
7 purchase totals =	$936.54		$1,020.9435	$1,020.95	$1,021.00	$1,021.00