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	$246.47	11.362%	$274.4739	$274.47	$274.45	$274.50
Purchase #2	$75.38	7.292%	$80.8767	$80.88	$80.90	$80.90
Purchase #3	$41.45	4.734%	$43.4122	$43.41	$43.40	$43.40
Purchase #4	$174.41	10.779%	$193.2097	$193.21	$193.20	$193.20
Purchase #5	$215.54	3.727%	$223.5732	$223.57	$223.55	$223.60
Purchase #6	$119.61	8.145%	$129.3522	$129.35	$129.35	$129.40
Purchase #7	$172.87	13.757%	$196.6517	$196.65	$196.65	$196.70
7 purchase totals =	$1,045.73		$1,141.5496	$1,141.54	$1,141.50	$1,141.70