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	$222.59	12.401%	$250.1934	$250.19	$250.20	$250.20
Purchase #2	$127.73	9.271%	$139.5718	$139.57	$139.55	$139.60
Purchase #3	$32.62	8.112%	$35.2661	$35.27	$35.25	$35.30
Purchase #4	$7.73	9.623%	$8.4739	$8.47	$8.45	$8.50
Purchase #5	$137.30	11.306%	$152.8231	$152.82	$152.80	$152.80
Purchase #6	$84.35	7.857%	$90.9774	$90.98	$91.00	$91.00
Purchase #7	$72.66	8.117%	$78.5578	$78.56	$78.55	$78.60
7 purchase totals =	$684.98		$755.8635	$755.86	$755.80	$756.00