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	$239.84	8.109%	$259.2886	$259.29	$259.30	$259.30
Purchase #2	$177.83	8.184%	$192.3836	$192.38	$192.40	$192.40
Purchase #3	$83.92	8.751%	$91.2638	$91.26	$91.25	$91.30
Purchase #4	$72.82	9.872%	$80.0088	$80.01	$80.00	$80.00
Purchase #5	$96.37	8.340%	$104.4073	$104.41	$104.40	$104.40
Purchase #6	$65.44	11.416%	$72.9106	$72.91	$72.90	$72.90
Purchase #7	$82.92	9.391%	$90.707	$90.71	$90.70	$90.70
7 purchase totals =	$819.14		$890.9697	$890.97	$890.95	$891.00