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	$218.43	11.661%	$243.9011	$243.90	$243.90	$243.90
Purchase #2	$81.98	10.140%	$90.2928	$90.29	$90.30	$90.30
Purchase #3	$172.25	6.150%	$182.8434	$182.84	$182.85	$182.80
Purchase #4	$135.41	11.288%	$150.6951	$150.70	$150.70	$150.70
Purchase #5	$5.85	4.147%	$6.0926	$6.09	$6.10	$6.10
Purchase #6	$115.69	10.836%	$128.2262	$128.23	$128.25	$128.20
Purchase #7	$17.48	13.833%	$19.898	$19.90	$19.90	$19.90
7 purchase totals =	$747.09		$821.9492	$821.95	$822.00	$821.90