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	$125.55	12.340%	$141.0429	$141.04	$141.05	$141.00
Purchase #2	$123.37	13.329%	$139.814	$139.81	$139.80	$139.80
Purchase #3	$90.62	10.308%	$99.9611	$99.96	$99.95	$100.00
Purchase #4	$95.31	8.827%	$103.723	$103.72	$103.70	$103.70
Purchase #5	$125.36	13.233%	$141.9489	$141.95	$141.95	$141.90
Purchase #6	$110.96	8.853%	$120.7833	$120.78	$120.80	$120.80
Purchase #7	$124.44	3.290%	$128.5341	$128.53	$128.55	$128.50
7 purchase totals =	$795.61		$875.8073	$875.79	$875.80	$875.70