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	$216.29	12.737%	$243.8389	$243.84	$243.85	$243.80
Purchase #2	$131.84	5.529%	$139.1294	$139.13	$139.15	$139.10
Purchase #3	$120.68	10.856%	$133.781	$133.78	$133.80	$133.80
Purchase #4	$29.97	7.550%	$32.2327	$32.23	$32.25	$32.20
Purchase #5	$73.56	6.356%	$78.2355	$78.24	$78.25	$78.20
Purchase #6	$163.55	13.113%	$184.9963	$185.00	$185.00	$185.00
Purchase #7	$42.45	7.850%	$45.7823	$45.78	$45.80	$45.80
7 purchase totals =	$778.34		$857.9961	$858.00	$858.10	$857.90