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	$129.45	12.282%	$145.349	$145.35	$145.35	$145.30
Purchase #2	$59.51	9.124%	$64.9397	$64.94	$64.95	$64.90
Purchase #3	$190.65	11.441%	$212.4623	$212.46	$212.45	$212.50
Purchase #4	$73.72	12.586%	$82.9984	$83.00	$83.00	$83.00
Purchase #5	$96.43	7.629%	$103.7866	$103.79	$103.80	$103.80
Purchase #6	$76.71	4.141%	$79.8866	$79.89	$79.90	$79.90
Purchase #7	$133.93	9.333%	$146.4297	$146.43	$146.45	$146.40
7 purchase totals =	$760.40		$835.8523	$835.86	$835.90	$835.80