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	$59.70	5.366%	$62.9035	$62.90	$62.90	$62.90
Purchase #2	$50.60	7.497%	$54.3935	$54.39	$54.40	$54.40
Purchase #3	$92.34	6.797%	$98.6163	$98.62	$98.60	$98.60
Purchase #4	$184.29	13.340%	$208.8743	$208.87	$208.85	$208.90
Purchase #5	$167.98	8.593%	$182.4145	$182.41	$182.40	$182.40
Purchase #6	$37.74	10.813%	$41.8208	$41.82	$41.80	$41.80
Purchase #7	$166.42	5.668%	$175.8527	$175.85	$175.85	$175.90
7 purchase totals =	$759.07		$824.8756	$824.86	$824.80	$824.90