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	$27.62	13.742%	$31.4155	$31.42	$31.40	$31.40
Purchase #2	$168.93	12.145%	$189.4465	$189.45	$189.45	$189.40
Purchase #3	$240.87	8.706%	$261.8401	$261.84	$261.85	$261.80
Purchase #4	$38.33	5.823%	$40.562	$40.56	$40.55	$40.60
Purchase #5	$39.28	8.745%	$42.715	$42.72	$42.70	$42.70
Purchase #6	$72.36	13.290%	$81.9766	$81.98	$82.00	$82.00
Purchase #7	$11.85	12.666%	$13.3509	$13.35	$13.35	$13.40
7 purchase totals =	$599.24		$661.3066	$661.32	$661.30	$661.30