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	$180.61	6.259%	$191.9144	$191.91	$191.90	$191.90
Purchase #2	$240.34	8.649%	$261.127	$261.13	$261.15	$261.10
Purchase #3	$172.65	13.759%	$196.4049	$196.40	$196.40	$196.40
Purchase #4	$133.77	8.620%	$145.301	$145.30	$145.30	$145.30
Purchase #5	$210.56	3.738%	$218.4307	$218.43	$218.45	$218.40
Purchase #6	$203.98	3.499%	$211.1173	$211.12	$211.10	$211.10
Purchase #7	$48.81	12.549%	$54.9352	$54.94	$54.95	$54.90
7 purchase totals =	$1,190.72		$1,279.2305	$1,279.23	$1,279.25	$1,279.10