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	$187.47	12.496%	$210.8963	$210.90	$210.90	$210.90
Purchase #2	$18.43	13.831%	$20.9791	$20.98	$21.00	$21.00
Purchase #3	$78.33	9.391%	$85.686	$85.69	$85.70	$85.70
Purchase #4	$155.96	4.397%	$162.8176	$162.82	$162.80	$162.80
Purchase #5	$208.27	8.382%	$225.7272	$225.73	$225.75	$225.70
Purchase #6	$161.82	3.780%	$167.9368	$167.94	$167.95	$167.90
Purchase #7	$157.55	5.133%	$165.637	$165.64	$165.65	$165.60
7 purchase totals =	$967.83		$1,039.6800	$1,039.70	$1,039.75	$1,039.60