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	$47.82	6.433%	$50.8963	$50.90	$50.90	$50.90
Purchase #2	$21.86	9.604%	$23.9594	$23.96	$23.95	$24.00
Purchase #3	$121.90	8.732%	$132.5443	$132.54	$132.55	$132.50
Purchase #4	$87.50	3.400%	$90.475	$90.48	$90.50	$90.50
Purchase #5	$157.33	5.581%	$166.1106	$166.11	$166.10	$166.10
Purchase #6	$39.36	3.508%	$40.7407	$40.74	$40.75	$40.70
Purchase #7	$67.44	5.362%	$71.0561	$71.06	$71.05	$71.10
7 purchase totals =	$543.21		$575.7824	$575.79	$575.80	$575.80