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	$85.74	5.328%	$90.3082	$90.31	$90.30	$90.30
Purchase #2	$96.92	9.639%	$106.2621	$106.26	$106.25	$106.30
Purchase #3	$131.48	12.800%	$148.3094	$148.31	$148.30	$148.30
Purchase #4	$167.59	12.529%	$188.5874	$188.59	$188.60	$188.60
Purchase #5	$127.78	7.280%	$137.0824	$137.08	$137.10	$137.10
Purchase #6	$234.96	7.867%	$253.4443	$253.44	$253.45	$253.40
Purchase #7	$28.96	6.399%	$30.8132	$30.81	$30.80	$30.80
7 purchase totals =	$873.43		$954.8070	$954.80	$954.80	$954.80