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	$182.37	3.800%	$189.3001	$189.30	$189.30	$189.30
Purchase #2	$67.32	6.764%	$71.8735	$71.87	$71.85	$71.90
Purchase #3	$105.87	10.402%	$116.8826	$116.88	$116.90	$116.90
Purchase #4	$109.97	8.111%	$118.8897	$118.89	$118.90	$118.90
Purchase #5	$74.93	7.578%	$80.6082	$80.61	$80.60	$80.60
Purchase #6	$205.96	5.665%	$217.6276	$217.63	$217.65	$217.60
Purchase #7	$153.91	4.153%	$160.3019	$160.30	$160.30	$160.30
7 purchase totals =	$900.33		$955.4836	$955.48	$955.50	$955.50