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	$37.96	7.780%	$40.9133	$40.91	$40.90	$40.90
Purchase #2	$62.36	12.555%	$70.1893	$70.19	$70.20	$70.20
Purchase #3	$212.47	7.312%	$228.0058	$228.01	$228.00	$228.00
Purchase #4	$187.69	12.732%	$211.5867	$211.59	$211.60	$211.60
Purchase #5	$52.31	13.730%	$59.4922	$59.49	$59.50	$59.50
Purchase #6	$152.73	4.548%	$159.6762	$159.68	$159.70	$159.70
Purchase #7	$31.55	6.455%	$33.5866	$33.59	$33.60	$33.60
7 purchase totals =	$737.07		$803.4501	$803.46	$803.50	$803.50