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	$82.33	6.793%	$87.9227	$87.92	$87.90	$87.90
Purchase #2	$141.41	12.588%	$159.2107	$159.21	$159.20	$159.20
Purchase #3	$240.91	5.160%	$253.341	$253.34	$253.35	$253.30
Purchase #4	$12.66	10.243%	$13.9568	$13.96	$13.95	$14.00
Purchase #5	$208.25	3.871%	$216.3114	$216.31	$216.30	$216.30
Purchase #6	$54.27	9.419%	$59.3817	$59.38	$59.40	$59.40
Purchase #7	$136.47	3.711%	$141.5344	$141.53	$141.55	$141.50
7 purchase totals =	$876.30		$931.6587	$931.65	$931.65	$931.60