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	$123.41	10.759%	$136.6877	$136.69	$136.70	$136.70
Purchase #2	$53.28	12.179%	$59.769	$59.77	$59.75	$59.80
Purchase #3	$222.94	13.609%	$253.2799	$253.28	$253.30	$253.30
Purchase #4	$242.84	13.259%	$275.0382	$275.04	$275.05	$275.00
Purchase #5	$62.56	13.308%	$70.8855	$70.89	$70.90	$70.90
Purchase #6	$59.27	7.207%	$63.5416	$63.54	$63.55	$63.50
Purchase #7	$90.33	6.393%	$96.1048	$96.10	$96.10	$96.10
7 purchase totals =	$854.63		$955.3067	$955.31	$955.35	$955.30