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	$43.91	11.574%	$48.9921	$48.99	$49.00	$49.00
Purchase #2	$80.90	10.682%	$89.5417	$89.54	$89.55	$89.50
Purchase #3	$181.53	9.230%	$198.2852	$198.29	$198.30	$198.30
Purchase #4	$178.89	11.191%	$198.9096	$198.91	$198.90	$198.90
Purchase #5	$86.31	3.116%	$88.9994	$89.00	$89.00	$89.00
Purchase #6	$163.84	3.867%	$170.1757	$170.18	$170.20	$170.20
Purchase #7	$56.35	4.703%	$59.0001	$59.00	$59.00	$59.00
7 purchase totals =	$791.73		$853.9038	$853.91	$853.95	$853.90