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	$92.36	7.580%	$99.3609	$99.36	$99.35	$99.40
Purchase #2	$31.31	6.410%	$33.317	$33.32	$33.30	$33.30
Purchase #3	$115.64	6.800%	$123.5035	$123.50	$123.50	$123.50
Purchase #4	$247.74	12.255%	$278.1005	$278.10	$278.10	$278.10
Purchase #5	$39.37	3.637%	$40.8019	$40.80	$40.80	$40.80
Purchase #6	$81.70	8.788%	$88.8798	$88.88	$88.90	$88.90
Purchase #7	$218.65	12.665%	$246.342	$246.34	$246.35	$246.30
7 purchase totals =	$826.77		$910.3056	$910.30	$910.30	$910.30