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	$131.54	4.267%	$137.1528	$137.15	$137.15	$137.20
Purchase #2	$93.27	6.554%	$99.3829	$99.38	$99.40	$99.40
Purchase #3	$191.46	12.342%	$215.09	$215.09	$215.10	$215.10
Purchase #4	$63.56	12.735%	$71.6544	$71.65	$71.65	$71.70
Purchase #5	$101.90	7.565%	$109.6087	$109.61	$109.60	$109.60
Purchase #6	$187.91	12.706%	$211.7858	$211.79	$211.80	$211.80
Purchase #7	$136.80	8.220%	$148.045	$148.05	$148.05	$148.00
7 purchase totals =	$906.44		$992.7196	$992.72	$992.75	$992.80