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	$178.90	6.750%	$190.9758	$190.98	$191.00	$191.00
Purchase #2	$135.73	10.845%	$150.4499	$150.45	$150.45	$150.40
Purchase #3	$81.31	11.301%	$90.4988	$90.50	$90.50	$90.50
Purchase #4	$25.40	12.845%	$28.6626	$28.66	$28.65	$28.70
Purchase #5	$245.48	10.623%	$271.5573	$271.56	$271.55	$271.60
Purchase #6	$154.34	7.651%	$166.1486	$166.15	$166.15	$166.10
Purchase #7	$31.73	12.299%	$35.6325	$35.63	$35.65	$35.60
7 purchase totals =	$852.89		$933.9255	$933.93	$933.95	$933.90