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	$233.35	6.788%	$249.1898	$249.19	$249.20	$249.20
Purchase #2	$77.25	8.369%	$83.7151	$83.72	$83.70	$83.70
Purchase #3	$161.48	11.672%	$180.3279	$180.33	$180.35	$180.30
Purchase #4	$12.43	9.342%	$13.5912	$13.59	$13.60	$13.60
Purchase #5	$140.90	12.242%	$158.149	$158.15	$158.15	$158.10
Purchase #6	$243.59	4.438%	$254.4005	$254.40	$254.40	$254.40
Purchase #7	$67.25	6.375%	$71.5372	$71.54	$71.55	$71.50
7 purchase totals =	$936.25		$1,010.9107	$1,010.92	$1,010.95	$1,010.80