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	$162.36	12.463%	$182.5949	$182.59	$182.60	$182.60
Purchase #2	$31.28	5.558%	$33.0185	$33.02	$33.00	$33.00
Purchase #3	$45.62	13.753%	$51.8941	$51.89	$51.90	$51.90
Purchase #4	$99.60	4.759%	$104.34	$104.34	$104.35	$104.30
Purchase #5	$81.95	10.524%	$90.5744	$90.57	$90.55	$90.60
Purchase #6	$93.77	6.110%	$99.4993	$99.50	$99.50	$99.50
Purchase #7	$35.77	9.706%	$39.2418	$39.24	$39.25	$39.20
7 purchase totals =	$550.35		$601.1630	$601.15	$601.15	$601.10