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	$131.96	3.235%	$136.2289	$136.23	$136.25	$136.20
Purchase #2	$105.59	11.837%	$118.0887	$118.09	$118.10	$118.10
Purchase #3	$59.40	6.544%	$63.2871	$63.29	$63.30	$63.30
Purchase #4	$213.76	11.743%	$238.8618	$238.86	$238.85	$238.90
Purchase #5	$48.37	3.616%	$50.1191	$50.12	$50.10	$50.10
Purchase #6	$186.54	6.221%	$198.1447	$198.14	$198.15	$198.10
Purchase #7	$148.89	11.503%	$166.0168	$166.02	$166.00	$166.00
7 purchase totals =	$894.51		$970.7471	$970.75	$970.75	$970.70