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	$234.81	12.799%	$264.8633	$264.86	$264.85	$264.90
Purchase #2	$131.69	4.657%	$137.8228	$137.82	$137.80	$137.80
Purchase #3	$7.34	4.251%	$7.652	$7.65	$7.65	$7.70
Purchase #4	$159.95	12.673%	$180.2205	$180.22	$180.20	$180.20
Purchase #5	$26.32	5.298%	$27.7144	$27.71	$27.70	$27.70
Purchase #6	$82.88	9.203%	$90.5074	$90.51	$90.50	$90.50
Purchase #7	$12.89	7.578%	$13.8668	$13.87	$13.85	$13.90
7 purchase totals =	$655.88		$722.6472	$722.64	$722.55	$722.70