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	$28.93	8.423%	$31.3668	$31.37	$31.35	$31.40
Purchase #2	$19.78	7.526%	$21.2686	$21.27	$21.25	$21.30
Purchase #3	$152.86	4.404%	$159.592	$159.59	$159.60	$159.60
Purchase #4	$84.42	3.760%	$87.5942	$87.59	$87.60	$87.60
Purchase #5	$109.47	10.449%	$120.9085	$120.91	$120.90	$120.90
Purchase #6	$75.77	12.661%	$85.3632	$85.36	$85.35	$85.40
Purchase #7	$219.94	10.331%	$242.662	$242.66	$242.65	$242.70
7 purchase totals =	$691.17		$748.7553	$748.75	$748.70	$748.90