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	$75.96	3.440%	$78.573	$78.57	$78.55	$78.60
Purchase #2	$187.31	11.720%	$209.2627	$209.26	$209.25	$209.30
Purchase #3	$42.33	6.660%	$45.1492	$45.15	$45.15	$45.10
Purchase #4	$145.59	9.409%	$159.2886	$159.29	$159.30	$159.30
Purchase #5	$76.34	11.613%	$85.2054	$85.21	$85.20	$85.20
Purchase #6	$176.95	9.820%	$194.3265	$194.33	$194.35	$194.30
Purchase #7	$224.95	9.199%	$245.6432	$245.64	$245.65	$245.60
7 purchase totals =	$929.43		$1,017.4486	$1,017.45	$1,017.45	$1,017.40