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	$81.48	12.272%	$91.4792	$91.48	$91.50	$91.50
Purchase #2	$85.62	4.266%	$89.2725	$89.27	$89.25	$89.30
Purchase #3	$139.61	3.582%	$144.6108	$144.61	$144.60	$144.60
Purchase #4	$62.77	8.386%	$68.0339	$68.03	$68.05	$68.00
Purchase #5	$114.37	4.347%	$119.3417	$119.34	$119.35	$119.30
Purchase #6	$170.40	9.830%	$187.1503	$187.15	$187.15	$187.20
Purchase #7	$125.80	9.179%	$137.3472	$137.35	$137.35	$137.30
7 purchase totals =	$780.05		$837.2356	$837.23	$837.25	$837.20