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	$121.47	5.713%	$128.4096	$128.41	$128.40	$128.40
Purchase #2	$239.48	8.504%	$259.8454	$259.85	$259.85	$259.80
Purchase #3	$85.78	12.154%	$96.2057	$96.21	$96.20	$96.20
Purchase #4	$137.33	11.315%	$152.8689	$152.87	$152.85	$152.90
Purchase #5	$235.82	3.502%	$244.0784	$244.08	$244.10	$244.10
Purchase #6	$131.96	13.831%	$150.2114	$150.21	$150.20	$150.20
Purchase #7	$64.69	5.789%	$68.4349	$68.43	$68.45	$68.40
7 purchase totals =	$1,016.53		$1,100.0543	$1,100.06	$1,100.05	$1,100.00