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	$113.25	6.741%	$120.8842	$120.88	$120.90	$120.90
Purchase #2	$196.27	6.817%	$209.6497	$209.65	$209.65	$209.60
Purchase #3	$249.93	11.400%	$278.422	$278.42	$278.40	$278.40
Purchase #4	$118.41	10.856%	$131.2646	$131.26	$131.25	$131.30
Purchase #5	$141.42	13.263%	$160.1765	$160.18	$160.20	$160.20
Purchase #6	$239.72	9.218%	$261.8174	$261.82	$261.80	$261.80
Purchase #7	$78.58	5.795%	$83.1337	$83.13	$83.15	$83.10
7 purchase totals =	$1,137.58		$1,245.3481	$1,245.34	$1,245.35	$1,245.30