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	$70.67	8.640%	$76.7759	$76.78	$76.80	$76.80
Purchase #2	$132.75	5.520%	$140.0778	$140.08	$140.10	$140.10
Purchase #3	$142.34	13.843%	$162.0441	$162.04	$162.05	$162.00
Purchase #4	$192.73	8.851%	$209.7885	$209.79	$209.80	$209.80
Purchase #5	$83.96	6.404%	$89.3368	$89.34	$89.35	$89.30
Purchase #6	$216.39	5.282%	$227.8197	$227.82	$227.80	$227.80
Purchase #7	$69.93	4.216%	$72.8782	$72.88	$72.90	$72.90
7 purchase totals =	$908.77		$978.7210	$978.73	$978.80	$978.70