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	$95.84	4.223%	$99.8873	$99.89	$99.90	$99.90
Purchase #2	$243.44	4.858%	$255.2663	$255.27	$255.25	$255.30
Purchase #3	$141.91	6.411%	$151.0079	$151.01	$151.00	$151.00
Purchase #4	$245.59	11.442%	$273.6904	$273.69	$273.70	$273.70
Purchase #5	$72.41	8.286%	$78.4099	$78.41	$78.40	$78.40
Purchase #6	$138.63	13.309%	$157.0803	$157.08	$157.10	$157.10
Purchase #7	$235.83	5.444%	$248.6686	$248.67	$248.65	$248.70
7 purchase totals =	$1,173.65		$1,264.0107	$1,264.02	$1,264.00	$1,264.10