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	$27.81	13.264%	$31.4987	$31.50	$31.50	$31.50
Purchase #2	$168.35	8.178%	$182.1177	$182.12	$182.10	$182.10
Purchase #3	$239.40	13.536%	$271.8052	$271.81	$271.80	$271.80
Purchase #4	$38.76	9.482%	$42.4352	$42.44	$42.45	$42.40
Purchase #5	$134.43	9.607%	$147.3447	$147.34	$147.35	$147.30
Purchase #6	$64.36	13.193%	$72.851	$72.85	$72.85	$72.90
Purchase #7	$209.82	10.628%	$232.1197	$232.12	$232.10	$232.10
7 purchase totals =	$882.93		$980.1722	$980.18	$980.15	$980.10