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	$39.89	4.300%	$41.6053	$41.61	$41.60	$41.60
Purchase #2	$227.63	5.529%	$240.2157	$240.22	$240.20	$240.20
Purchase #3	$179.53	3.184%	$185.2462	$185.25	$185.25	$185.20
Purchase #4	$218.97	8.604%	$237.8102	$237.81	$237.80	$237.80
Purchase #5	$83.54	10.755%	$92.5247	$92.52	$92.50	$92.50
Purchase #6	$13.44	9.622%	$14.7332	$14.73	$14.75	$14.70
Purchase #7	$89.72	11.591%	$100.1194	$100.12	$100.10	$100.10
7 purchase totals =	$852.72		$912.2547	$912.26	$912.20	$912.10