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	$84.74	8.430%	$91.8836	$91.88	$91.90	$91.90
Purchase #2	$240.84	13.232%	$272.7079	$272.71	$272.70	$272.70
Purchase #3	$173.81	10.224%	$191.5803	$191.58	$191.60	$191.60
Purchase #4	$127.81	13.620%	$145.2177	$145.22	$145.20	$145.20
Purchase #5	$243.47	11.134%	$270.5779	$270.58	$270.60	$270.60
Purchase #6	$32.34	6.362%	$34.3975	$34.40	$34.40	$34.40
Purchase #7	$31.63	5.849%	$33.48	$33.48	$33.50	$33.50
7 purchase totals =	$934.64		$1,039.8449	$1,039.85	$1,039.90	$1,039.90