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	$63.89	6.128%	$67.8052	$67.81	$67.80	$67.80
Purchase #2	$89.66	3.661%	$92.9425	$92.94	$92.95	$92.90
Purchase #3	$192.77	8.534%	$209.221	$209.22	$209.20	$209.20
Purchase #4	$96.93	13.320%	$109.8411	$109.84	$109.85	$109.80
Purchase #5	$52.71	12.150%	$59.1143	$59.11	$59.10	$59.10
Purchase #6	$100.54	12.181%	$112.7868	$112.79	$112.80	$112.80
Purchase #7	$80.34	7.324%	$86.2241	$86.22	$86.20	$86.20
7 purchase totals =	$676.84		$737.9350	$737.93	$737.90	$737.80