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	$193.82	5.130%	$203.763	$203.76	$203.75	$203.80
Purchase #2	$149.74	11.869%	$167.5126	$167.51	$167.50	$167.50
Purchase #3	$244.83	12.646%	$275.7912	$275.79	$275.80	$275.80
Purchase #4	$43.43	5.750%	$45.9272	$45.93	$45.95	$45.90
Purchase #5	$149.69	8.525%	$162.4511	$162.45	$162.45	$162.50
Purchase #6	$5.50	6.538%	$5.8596	$5.86	$5.85	$5.90
Purchase #7	$37.36	8.504%	$40.5371	$40.54	$40.55	$40.50
7 purchase totals =	$824.37		$901.8418	$901.84	$901.85	$901.90