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	$208.93	12.426%	$234.8916	$234.89	$234.90	$234.90
Purchase #2	$44.34	4.472%	$46.3229	$46.32	$46.30	$46.30
Purchase #3	$132.78	6.569%	$141.5023	$141.50	$141.50	$141.50
Purchase #4	$30.63	8.506%	$33.2354	$33.24	$33.25	$33.20
Purchase #5	$28.58	9.769%	$31.372	$31.37	$31.35	$31.40
Purchase #6	$222.62	10.207%	$245.3428	$245.34	$245.35	$245.30
Purchase #7	$225.65	9.148%	$246.2925	$246.29	$246.30	$246.30
7 purchase totals =	$893.53		$978.9595	$978.95	$978.95	$978.90