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	$125.27	13.158%	$141.753	$141.75	$141.75	$141.80
Purchase #2	$143.79	8.278%	$155.6929	$155.69	$155.70	$155.70
Purchase #3	$73.35	12.444%	$82.4777	$82.48	$82.50	$82.50
Purchase #4	$94.73	10.850%	$105.0082	$105.01	$105.00	$105.00
Purchase #5	$29.50	13.507%	$33.4846	$33.48	$33.50	$33.50
Purchase #6	$170.34	6.113%	$180.7529	$180.75	$180.75	$180.80
Purchase #7	$211.25	3.372%	$218.3734	$218.37	$218.35	$218.40
7 purchase totals =	$848.23		$917.5427	$917.53	$917.55	$917.70