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	$8.35	10.362%	$9.2152	$9.22	$9.20	$9.20
Purchase #2	$179.76	9.127%	$196.1667	$196.17	$196.15	$196.20
Purchase #3	$189.61	9.767%	$208.1292	$208.13	$208.15	$208.10
Purchase #4	$199.44	8.394%	$216.181	$216.18	$216.20	$216.20
Purchase #5	$33.72	9.825%	$37.033	$37.03	$37.05	$37.00
Purchase #6	$110.78	9.132%	$120.8964	$120.90	$120.90	$120.90
Purchase #7	$65.39	11.509%	$72.9157	$72.92	$72.90	$72.90
7 purchase totals =	$787.05		$860.5372	$860.55	$860.55	$860.50