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	$55.43	12.373%	$62.2884	$62.29	$62.30	$62.30
Purchase #2	$227.88	11.245%	$253.5051	$253.51	$253.50	$253.50
Purchase #3	$240.41	12.530%	$270.5334	$270.53	$270.55	$270.50
Purchase #4	$41.97	7.267%	$45.02	$45.02	$45.00	$45.00
Purchase #5	$53.64	3.513%	$55.5244	$55.52	$55.50	$55.50
Purchase #6	$63.58	6.264%	$67.5627	$67.56	$67.55	$67.60
Purchase #7	$63.47	5.725%	$67.1037	$67.10	$67.10	$67.10
7 purchase totals =	$746.38		$821.5377	$821.53	$821.50	$821.50