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	$113.35	9.590%	$124.2203	$124.22	$124.20	$124.20
Purchase #2	$83.72	8.129%	$90.5256	$90.53	$90.55	$90.50
Purchase #3	$248.71	12.772%	$280.4752	$280.48	$280.50	$280.50
Purchase #4	$152.78	9.413%	$167.1612	$167.16	$167.15	$167.20
Purchase #5	$88.76	9.742%	$97.407	$97.41	$97.40	$97.40
Purchase #6	$72.78	7.756%	$78.4248	$78.42	$78.40	$78.40
Purchase #7	$140.30	13.715%	$159.5421	$159.54	$159.55	$159.50
7 purchase totals =	$900.40		$997.7562	$997.76	$997.75	$997.70