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	$67.27	6.122%	$71.3883	$71.39	$71.40	$71.40
Purchase #2	$115.87	3.447%	$119.864	$119.86	$119.85	$119.90
Purchase #3	$97.50	11.841%	$109.045	$109.05	$109.05	$109.00
Purchase #4	$32.58	3.261%	$33.6424	$33.64	$33.65	$33.60
Purchase #5	$52.93	11.252%	$58.8857	$58.89	$58.90	$58.90
Purchase #6	$50.26	5.410%	$52.9791	$52.98	$53.00	$53.00
Purchase #7	$86.49	9.309%	$94.5414	$94.54	$94.55	$94.50
7 purchase totals =	$502.90		$540.3459	$540.35	$540.40	$540.30