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	$31.33	4.689%	$32.7991	$32.80	$32.80	$32.80
Purchase #2	$80.86	10.684%	$89.4991	$89.50	$89.50	$89.50
Purchase #3	$41.51	5.640%	$43.8512	$43.85	$43.85	$43.90
Purchase #4	$93.75	4.818%	$98.2669	$98.27	$98.25	$98.30
Purchase #5	$63.99	11.610%	$71.4192	$71.42	$71.40	$71.40
Purchase #6	$130.95	5.313%	$137.9074	$137.91	$137.90	$137.90
Purchase #7	$194.94	12.451%	$219.212	$219.21	$219.20	$219.20
7 purchase totals =	$637.33		$692.9549	$692.96	$692.90	$693.00