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	$5.91	8.287%	$6.3998	$6.40	$6.40	$6.40
Purchase #2	$55.95	12.531%	$62.9611	$62.96	$62.95	$63.00
Purchase #3	$170.84	8.490%	$185.3443	$185.34	$185.35	$185.30
Purchase #4	$52.47	10.663%	$58.0649	$58.06	$58.05	$58.10
Purchase #5	$155.42	10.213%	$171.293	$171.29	$171.30	$171.30
Purchase #6	$243.32	11.347%	$270.9295	$270.93	$270.95	$270.90
Purchase #7	$233.31	6.520%	$248.5218	$248.52	$248.50	$248.50
7 purchase totals =	$917.22		$1,003.5144	$1,003.50	$1,003.50	$1,003.50