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	$171.88	9.551%	$188.2963	$188.30	$188.30	$188.30
Purchase #2	$170.95	11.628%	$190.8281	$190.83	$190.85	$190.80
Purchase #3	$82.54	7.615%	$88.8254	$88.83	$88.85	$88.80
Purchase #4	$181.81	3.614%	$188.3806	$188.38	$188.40	$188.40
Purchase #5	$185.88	5.582%	$196.2558	$196.26	$196.25	$196.30
Purchase #6	$24.91	13.185%	$28.1944	$28.19	$28.20	$28.20
Purchase #7	$173.41	5.728%	$183.3429	$183.34	$183.35	$183.30
7 purchase totals =	$991.38		$1,064.1235	$1,064.13	$1,064.20	$1,064.10