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	$55.73	6.503%	$59.3541	$59.35	$59.35	$59.40
Purchase #2	$39.41	9.601%	$43.1938	$43.19	$43.20	$43.20
Purchase #3	$108.52	3.651%	$112.4821	$112.48	$112.50	$112.50
Purchase #4	$116.33	13.507%	$132.0427	$132.04	$132.05	$132.00
Purchase #5	$96.34	13.102%	$108.9625	$108.96	$108.95	$109.00
Purchase #6	$15.92	10.282%	$17.5569	$17.56	$17.55	$17.60
Purchase #7	$21.53	4.703%	$22.5426	$22.54	$22.55	$22.50
7 purchase totals =	$453.78		$496.1347	$496.12	$496.15	$496.20