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	$224.47	11.317%	$249.8733	$249.87	$249.85	$249.90
Purchase #2	$117.60	11.292%	$130.8794	$130.88	$130.90	$130.90
Purchase #3	$204.52	9.474%	$223.8962	$223.90	$223.90	$223.90
Purchase #4	$73.36	12.809%	$82.7567	$82.76	$82.75	$82.80
Purchase #5	$7.33	8.661%	$7.9649	$7.96	$7.95	$8.00
Purchase #6	$149.31	6.424%	$158.9017	$158.90	$158.90	$158.90
Purchase #7	$118.58	10.121%	$130.5815	$130.58	$130.60	$130.60
7 purchase totals =	$895.17		$984.8537	$984.85	$984.85	$985.00