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	$57.56	12.614%	$64.8206	$64.82	$64.80	$64.80
Purchase #2	$174.61	6.265%	$185.5493	$185.55	$185.55	$185.50
Purchase #3	$68.78	3.588%	$71.2478	$71.25	$71.25	$71.20
Purchase #4	$209.59	12.547%	$235.8873	$235.89	$235.90	$235.90
Purchase #5	$155.71	6.341%	$165.5836	$165.58	$165.60	$165.60
Purchase #6	$67.48	12.107%	$75.6498	$75.65	$75.65	$75.60
Purchase #7	$31.86	7.409%	$34.2205	$34.22	$34.20	$34.20
7 purchase totals =	$765.59		$832.9589	$832.96	$832.95	$832.80