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	$80.63	12.790%	$90.9426	$90.94	$90.95	$90.90
Purchase #2	$196.29	6.225%	$208.5091	$208.51	$208.50	$208.50
Purchase #3	$90.53	9.578%	$99.201	$99.20	$99.20	$99.20
Purchase #4	$140.79	9.802%	$154.5902	$154.59	$154.60	$154.60
Purchase #5	$243.37	10.598%	$269.1624	$269.16	$269.15	$269.20
Purchase #6	$93.55	4.868%	$98.104	$98.10	$98.10	$98.10
Purchase #7	$72.96	5.862%	$77.2369	$77.24	$77.25	$77.20
7 purchase totals =	$918.12		$997.7462	$997.74	$997.75	$997.70