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	$89.61	4.428%	$93.5779	$93.58	$93.60	$93.60
Purchase #2	$51.93	8.760%	$56.4791	$56.48	$56.50	$56.50
Purchase #3	$227.57	12.427%	$255.8501	$255.85	$255.85	$255.90
Purchase #4	$80.34	11.535%	$89.6072	$89.61	$89.60	$89.60
Purchase #5	$227.33	4.664%	$237.9327	$237.93	$237.95	$237.90
Purchase #6	$157.73	13.353%	$178.7917	$178.79	$178.80	$178.80
Purchase #7	$6.89	12.675%	$7.7633	$7.76	$7.75	$7.80
7 purchase totals =	$841.40		$920.0020	$920.00	$920.05	$920.10