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	$85.82	7.356%	$92.1329	$92.13	$92.15	$92.10
Purchase #2	$40.82	5.843%	$43.2051	$43.21	$43.20	$43.20
Purchase #3	$78.90	12.800%	$88.9992	$89.00	$89.00	$89.00
Purchase #4	$54.83	13.479%	$62.2205	$62.22	$62.20	$62.20
Purchase #5	$250.69	7.746%	$270.1084	$270.11	$270.10	$270.10
Purchase #6	$62.69	13.604%	$71.2183	$71.22	$71.20	$71.20
Purchase #7	$112.78	5.605%	$119.1013	$119.10	$119.10	$119.10
7 purchase totals =	$686.53		$746.9857	$746.99	$746.95	$746.90