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	$220.81	12.553%	$248.5283	$248.53	$248.55	$248.50
Purchase #2	$218.91	10.673%	$242.2743	$242.27	$242.25	$242.30
Purchase #3	$40.25	4.864%	$42.2078	$42.21	$42.20	$42.20
Purchase #4	$68.58	5.165%	$72.1222	$72.12	$72.10	$72.10
Purchase #5	$25.50	11.705%	$28.4848	$28.48	$28.50	$28.50
Purchase #6	$196.52	13.764%	$223.569	$223.57	$223.55	$223.60
Purchase #7	$74.46	3.866%	$77.3386	$77.34	$77.35	$77.30
7 purchase totals =	$845.03		$934.5250	$934.52	$934.50	$934.50