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	$76.38	8.655%	$82.9907	$82.99	$83.00	$83.00
Purchase #2	$130.88	8.102%	$141.4839	$141.48	$141.50	$141.50
Purchase #3	$137.52	4.661%	$143.9298	$143.93	$143.95	$143.90
Purchase #4	$201.49	8.577%	$218.7718	$218.77	$218.75	$218.80
Purchase #5	$28.66	9.819%	$31.4741	$31.47	$31.45	$31.50
Purchase #6	$209.53	7.630%	$225.5171	$225.52	$225.50	$225.50
Purchase #7	$89.28	3.395%	$92.3111	$92.31	$92.30	$92.30
7 purchase totals =	$873.74		$936.4785	$936.47	$936.45	$936.50