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	$87.59	7.178%	$93.8772	$93.88	$93.90	$93.90
Purchase #2	$74.54	4.774%	$78.0985	$78.10	$78.10	$78.10
Purchase #3	$42.41	11.614%	$47.3355	$47.34	$47.35	$47.30
Purchase #4	$198.73	13.557%	$225.6718	$225.67	$225.65	$225.70
Purchase #5	$33.41	11.405%	$37.2204	$37.22	$37.20	$37.20
Purchase #6	$98.48	6.545%	$104.9255	$104.93	$104.95	$104.90
Purchase #7	$107.37	9.223%	$117.2727	$117.27	$117.25	$117.30
7 purchase totals =	$642.53		$704.4016	$704.41	$704.40	$704.40