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	$189.71	13.754%	$215.8027	$215.80	$215.80	$215.80
Purchase #2	$76.40	13.491%	$86.7071	$86.71	$86.70	$86.70
Purchase #3	$108.77	4.288%	$113.4341	$113.43	$113.45	$113.40
Purchase #4	$179.85	6.666%	$191.8388	$191.84	$191.85	$191.80
Purchase #5	$141.63	3.799%	$147.0105	$147.01	$147.00	$147.00
Purchase #6	$243.80	11.700%	$272.3246	$272.32	$272.30	$272.30
Purchase #7	$187.38	4.254%	$195.3511	$195.35	$195.35	$195.40
7 purchase totals =	$1,127.54		$1,222.4689	$1,222.46	$1,222.45	$1,222.40