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	$130.59	12.266%	$146.6082	$146.61	$146.60	$146.60
Purchase #2	$175.33	3.143%	$180.8406	$180.84	$180.85	$180.80
Purchase #3	$202.93	13.865%	$231.0662	$231.07	$231.05	$231.10
Purchase #4	$133.91	5.710%	$141.5563	$141.56	$141.55	$141.60
Purchase #5	$92.82	7.272%	$99.5699	$99.57	$99.55	$99.60
Purchase #6	$239.69	10.710%	$265.3608	$265.36	$265.35	$265.40
Purchase #7	$174.50	8.227%	$188.8561	$188.86	$188.85	$188.90
7 purchase totals =	$1,149.77		$1,253.8581	$1,253.87	$1,253.80	$1,254.00