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	$244.61	4.707%	$256.1238	$256.12	$256.10	$256.10
Purchase #2	$123.72	5.764%	$130.8512	$130.85	$130.85	$130.90
Purchase #3	$61.33	3.694%	$63.5955	$63.60	$63.60	$63.60
Purchase #4	$166.61	9.452%	$182.358	$182.36	$182.35	$182.40
Purchase #5	$85.28	6.734%	$91.0228	$91.02	$91.00	$91.00
Purchase #6	$95.48	9.811%	$104.8475	$104.85	$104.85	$104.80
Purchase #7	$141.86	9.134%	$154.8175	$154.82	$154.80	$154.80
7 purchase totals =	$918.89		$983.6163	$983.62	$983.55	$983.60