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	$23.34	3.602%	$24.1807	$24.18	$24.20	$24.20
Purchase #2	$38.51	9.232%	$42.0652	$42.07	$42.05	$42.10
Purchase #3	$185.44	12.597%	$208.7999	$208.80	$208.80	$208.80
Purchase #4	$83.75	6.544%	$89.2306	$89.23	$89.25	$89.20
Purchase #5	$207.98	5.109%	$218.6057	$218.61	$218.60	$218.60
Purchase #6	$98.39	10.859%	$109.0742	$109.07	$109.05	$109.10
Purchase #7	$57.38	6.486%	$61.1017	$61.10	$61.10	$61.10
7 purchase totals =	$694.79		$753.0580	$753.06	$753.05	$753.10