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	$122.47	12.385%	$137.6379	$137.64	$137.65	$137.60
Purchase #2	$94.67	11.416%	$105.4775	$105.48	$105.50	$105.50
Purchase #3	$90.81	7.282%	$97.4228	$97.42	$97.40	$97.40
Purchase #4	$71.66	6.781%	$76.5193	$76.52	$76.50	$76.50
Purchase #5	$97.42	8.277%	$105.4835	$105.48	$105.50	$105.50
Purchase #6	$244.34	8.558%	$265.2506	$265.25	$265.25	$265.30
Purchase #7	$77.66	12.726%	$87.543	$87.54	$87.55	$87.50
7 purchase totals =	$799.03		$875.3346	$875.33	$875.35	$875.30