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	$113.98	4.282%	$118.8606	$118.86	$118.85	$118.90
Purchase #2	$68.47	12.498%	$77.0274	$77.03	$77.05	$77.00
Purchase #3	$150.94	12.602%	$169.9615	$169.96	$169.95	$170.00
Purchase #4	$134.34	9.734%	$147.4167	$147.42	$147.40	$147.40
Purchase #5	$39.70	10.436%	$43.8431	$43.84	$43.85	$43.80
Purchase #6	$52.78	12.254%	$59.2477	$59.25	$59.25	$59.20
Purchase #7	$187.59	13.294%	$212.5282	$212.53	$212.55	$212.50
7 purchase totals =	$747.80		$828.8852	$828.89	$828.90	$828.80