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	$188.88	7.674%	$203.3747	$203.37	$203.35	$203.40
Purchase #2	$80.36	12.155%	$90.1278	$90.13	$90.15	$90.10
Purchase #3	$71.98	9.535%	$78.8433	$78.84	$78.85	$78.80
Purchase #4	$26.35	11.229%	$29.3088	$29.31	$29.30	$29.30
Purchase #5	$146.88	11.651%	$163.993	$163.99	$164.00	$164.00
Purchase #6	$174.85	9.473%	$191.4135	$191.41	$191.40	$191.40
Purchase #7	$123.51	4.362%	$128.8975	$128.90	$128.90	$128.90
7 purchase totals =	$812.81		$885.9586	$885.95	$885.95	$885.90