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	$7.35	5.797%	$7.7761	$7.78	$7.80	$7.80
Purchase #2	$93.89	10.695%	$103.9315	$103.93	$103.95	$103.90
Purchase #3	$123.33	3.440%	$127.5726	$127.57	$127.55	$127.60
Purchase #4	$43.84	3.123%	$45.2091	$45.21	$45.20	$45.20
Purchase #5	$180.91	9.846%	$198.7224	$198.72	$198.70	$198.70
Purchase #6	$57.76	10.454%	$63.7982	$63.80	$63.80	$63.80
Purchase #7	$209.54	13.473%	$237.7713	$237.77	$237.75	$237.80
7 purchase totals =	$716.62		$784.7812	$784.78	$784.75	$784.80