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	$248.47	10.801%	$275.3072	$275.31	$275.30	$275.30
Purchase #2	$85.77	9.506%	$93.9233	$93.92	$93.90	$93.90
Purchase #3	$196.65	6.803%	$210.0281	$210.03	$210.05	$210.00
Purchase #4	$37.29	9.472%	$40.8221	$40.82	$40.80	$40.80
Purchase #5	$28.81	3.820%	$29.9105	$29.91	$29.90	$29.90
Purchase #6	$147.33	4.569%	$154.0615	$154.06	$154.05	$154.10
Purchase #7	$239.28	9.867%	$262.8898	$262.89	$262.90	$262.90
7 purchase totals =	$983.60		$1,066.9425	$1,066.94	$1,066.90	$1,066.90