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	$72.90	12.859%	$82.2742	$82.27	$82.25	$82.30
Purchase #2	$36.96	11.147%	$41.0799	$41.08	$41.10	$41.10
Purchase #3	$94.56	11.112%	$105.0675	$105.07	$105.05	$105.10
Purchase #4	$119.61	13.581%	$135.8542	$135.85	$135.85	$135.90
Purchase #5	$43.72	9.308%	$47.7895	$47.79	$47.80	$47.80
Purchase #6	$112.76	5.387%	$118.8344	$118.83	$118.85	$118.80
Purchase #7	$76.27	10.518%	$84.2921	$84.29	$84.30	$84.30
7 purchase totals =	$556.78		$615.1918	$615.18	$615.20	$615.30