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	$59.54	3.822%	$61.8156	$61.82	$61.80	$61.80
Purchase #2	$209.82	7.487%	$225.5292	$225.53	$225.55	$225.50
Purchase #3	$245.43	6.869%	$262.2886	$262.29	$262.30	$262.30
Purchase #4	$30.80	11.224%	$34.257	$34.26	$34.25	$34.30
Purchase #5	$157.59	5.617%	$166.4418	$166.44	$166.45	$166.40
Purchase #6	$92.34	8.213%	$99.9239	$99.92	$99.90	$99.90
Purchase #7	$80.40	10.135%	$88.5485	$88.55	$88.55	$88.50
7 purchase totals =	$875.92		$938.8046	$938.81	$938.80	$938.70