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	$250.55	10.526%	$276.9229	$276.92	$276.90	$276.90
Purchase #2	$131.38	11.470%	$146.4493	$146.45	$146.45	$146.40
Purchase #3	$149.34	7.667%	$160.7899	$160.79	$160.80	$160.80
Purchase #4	$125.74	4.341%	$131.1984	$131.20	$131.20	$131.20
Purchase #5	$133.72	5.452%	$141.0104	$141.01	$141.00	$141.00
Purchase #6	$94.82	4.270%	$98.8688	$98.87	$98.85	$98.90
Purchase #7	$42.54	12.537%	$47.8732	$47.87	$47.85	$47.90
7 purchase totals =	$928.09		$1,003.1129	$1,003.11	$1,003.05	$1,003.10