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	$23.27	8.800%	$25.3178	$25.32	$25.30	$25.30
Purchase #2	$101.82	7.378%	$109.3323	$109.33	$109.35	$109.30
Purchase #3	$37.66	12.764%	$42.4669	$42.47	$42.45	$42.50
Purchase #4	$230.54	10.341%	$254.3801	$254.38	$254.40	$254.40
Purchase #5	$246.70	6.311%	$262.2692	$262.27	$262.25	$262.30
Purchase #6	$146.79	8.628%	$159.455	$159.46	$159.45	$159.50
Purchase #7	$37.71	5.365%	$39.7331	$39.73	$39.75	$39.70
7 purchase totals =	$824.49		$892.9544	$892.96	$892.95	$893.00