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	$40.72	6.309%	$43.289	$43.29	$43.30	$43.30
Purchase #2	$215.39	3.620%	$223.1871	$223.19	$223.20	$223.20
Purchase #3	$22.51	13.427%	$25.5324	$25.53	$25.55	$25.50
Purchase #4	$189.63	13.420%	$215.0783	$215.08	$215.10	$215.10
Purchase #5	$67.43	11.133%	$74.937	$74.94	$74.95	$74.90
Purchase #6	$81.41	12.247%	$91.3803	$91.38	$91.40	$91.40
Purchase #7	$165.40	10.572%	$182.8861	$182.89	$182.90	$182.90
7 purchase totals =	$782.49		$856.2902	$856.30	$856.40	$856.30