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	$116.42	4.480%	$121.6356	$121.64	$121.65	$121.60
Purchase #2	$67.89	9.865%	$74.5873	$74.59	$74.60	$74.60
Purchase #3	$55.49	7.334%	$59.5596	$59.56	$59.55	$59.60
Purchase #4	$249.73	9.766%	$274.1186	$274.12	$274.10	$274.10
Purchase #5	$37.33	4.361%	$38.958	$38.96	$38.95	$39.00
Purchase #6	$60.93	10.829%	$67.5281	$67.53	$67.55	$67.50
Purchase #7	$29.46	12.800%	$33.2309	$33.23	$33.25	$33.20
7 purchase totals =	$617.25		$669.6181	$669.63	$669.65	$669.60