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	$40.47	3.779%	$41.9994	$42.00	$42.00	$42.00
Purchase #2	$50.61	3.441%	$52.3515	$52.35	$52.35	$52.40
Purchase #3	$206.59	8.673%	$224.5076	$224.51	$224.50	$224.50
Purchase #4	$218.47	7.727%	$235.3512	$235.35	$235.35	$235.40
Purchase #5	$242.72	13.427%	$275.31	$275.31	$275.30	$275.30
Purchase #6	$100.98	13.266%	$114.376	$114.38	$114.40	$114.40
Purchase #7	$105.92	9.586%	$116.0735	$116.07	$116.05	$116.10
7 purchase totals =	$965.76		$1,059.9692	$1,059.97	$1,059.95	$1,060.10