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	$141.63	12.646%	$159.5405	$159.54	$159.55	$159.50
Purchase #2	$95.41	4.219%	$99.4353	$99.44	$99.45	$99.40
Purchase #3	$153.56	9.605%	$168.3094	$168.31	$168.30	$168.30
Purchase #4	$120.32	9.434%	$131.671	$131.67	$131.65	$131.70
Purchase #5	$212.48	9.676%	$233.0396	$233.04	$233.05	$233.00
Purchase #6	$128.96	9.199%	$140.823	$140.82	$140.80	$140.80
Purchase #7	$7.41	10.700%	$8.2029	$8.20	$8.20	$8.20
7 purchase totals =	$859.77		$941.0217	$941.02	$941.00	$940.90