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	$56.36	13.703%	$64.083	$64.08	$64.10	$64.10
Purchase #2	$206.62	7.772%	$222.6785	$222.68	$222.70	$222.70
Purchase #3	$86.57	4.604%	$90.5557	$90.56	$90.55	$90.60
Purchase #4	$78.53	8.533%	$85.231	$85.23	$85.25	$85.20
Purchase #5	$36.76	10.868%	$40.7551	$40.76	$40.75	$40.80
Purchase #6	$87.61	10.462%	$96.7758	$96.78	$96.80	$96.80
Purchase #7	$11.86	6.562%	$12.6383	$12.64	$12.65	$12.60
7 purchase totals =	$564.31		$612.7174	$612.73	$612.80	$612.80