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	$38.78	9.267%	$42.3737	$42.37	$42.35	$42.40
Purchase #2	$153.54	13.432%	$174.1635	$174.16	$174.15	$174.20
Purchase #3	$231.26	9.798%	$253.9189	$253.92	$253.90	$253.90
Purchase #4	$75.93	12.210%	$85.2011	$85.20	$85.20	$85.20
Purchase #5	$54.78	4.672%	$57.3393	$57.34	$57.35	$57.30
Purchase #6	$71.86	13.142%	$81.3038	$81.30	$81.30	$81.30
Purchase #7	$162.68	11.811%	$181.8941	$181.89	$181.90	$181.90
7 purchase totals =	$788.83		$876.1944	$876.18	$876.15	$876.20