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	$47.90	5.619%	$50.5915	$50.59	$50.60	$50.60
Purchase #2	$195.34	12.763%	$220.2712	$220.27	$220.25	$220.30
Purchase #3	$239.50	6.550%	$255.1873	$255.19	$255.20	$255.20
Purchase #4	$173.27	3.553%	$179.4263	$179.43	$179.45	$179.40
Purchase #5	$125.51	12.276%	$140.9176	$140.92	$140.90	$140.90
Purchase #6	$171.96	10.614%	$190.2118	$190.21	$190.20	$190.20
Purchase #7	$249.47	7.139%	$267.2797	$267.28	$267.30	$267.30
7 purchase totals =	$1,202.95		$1,303.8854	$1,303.89	$1,303.90	$1,303.90