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	$28.93	8.516%	$31.3937	$31.39	$31.40	$31.40
Purchase #2	$76.55	9.157%	$83.5597	$83.56	$83.55	$83.60
Purchase #3	$55.50	10.669%	$61.4213	$61.42	$61.40	$61.40
Purchase #4	$32.34	10.638%	$35.7803	$35.78	$35.80	$35.80
Purchase #5	$191.86	7.188%	$205.6509	$205.65	$205.65	$205.70
Purchase #6	$127.54	9.303%	$139.405	$139.41	$139.40	$139.40
Purchase #7	$7.63	6.484%	$8.1247	$8.12	$8.10	$8.10
7 purchase totals =	$520.35		$565.3356	$565.33	$565.30	$565.40