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	$56.36	5.208%	$59.2952	$59.30	$59.30	$59.30
Purchase #2	$136.43	10.688%	$151.0116	$151.01	$151.00	$151.00
Purchase #3	$101.36	13.767%	$115.3142	$115.31	$115.30	$115.30
Purchase #4	$229.85	13.106%	$259.9741	$259.97	$259.95	$260.00
Purchase #5	$223.83	10.616%	$247.5918	$247.59	$247.60	$247.60
Purchase #6	$109.34	11.489%	$121.9021	$121.90	$121.90	$121.90
Purchase #7	$155.68	13.588%	$176.8338	$176.83	$176.85	$176.80
7 purchase totals =	$1,012.85		$1,131.9228	$1,131.91	$1,131.90	$1,131.90