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	$136.72	9.588%	$149.8287	$149.83	$149.85	$149.80
Purchase #2	$110.99	5.230%	$116.7948	$116.79	$116.80	$116.80
Purchase #3	$147.58	4.868%	$154.7642	$154.76	$154.75	$154.80
Purchase #4	$31.80	6.353%	$33.8203	$33.82	$33.80	$33.80
Purchase #5	$54.52	9.294%	$59.5871	$59.59	$59.60	$59.60
Purchase #6	$56.43	4.287%	$58.8492	$58.85	$58.85	$58.80
Purchase #7	$69.26	5.165%	$72.8373	$72.84	$72.85	$72.80
7 purchase totals =	$607.30		$646.4816	$646.48	$646.50	$646.40