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	$162.56	3.865%	$168.8429	$168.84	$168.85	$168.80
Purchase #2	$245.52	11.257%	$273.1582	$273.16	$273.15	$273.20
Purchase #3	$110.67	9.802%	$121.5179	$121.52	$121.50	$121.50
Purchase #4	$131.64	9.787%	$144.5236	$144.52	$144.50	$144.50
Purchase #5	$30.95	5.204%	$32.5606	$32.56	$32.55	$32.60
Purchase #6	$50.93	4.630%	$53.2881	$53.29	$53.30	$53.30
Purchase #7	$165.56	12.293%	$185.9123	$185.91	$185.90	$185.90
7 purchase totals =	$897.83		$979.8036	$979.80	$979.75	$979.80