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	$118.94	10.585%	$131.5298	$131.53	$131.55	$131.50
Purchase #2	$22.44	10.529%	$24.8027	$24.80	$24.80	$24.80
Purchase #3	$250.61	10.628%	$277.2448	$277.24	$277.25	$277.20
Purchase #4	$37.49	5.598%	$39.5887	$39.59	$39.60	$39.60
Purchase #5	$137.62	7.419%	$147.83	$147.83	$147.85	$147.80
Purchase #6	$85.59	8.630%	$92.9764	$92.98	$93.00	$93.00
Purchase #7	$127.76	7.871%	$137.816	$137.82	$137.80	$137.80
7 purchase totals =	$780.45		$851.7884	$851.79	$851.85	$851.70