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	$144.37	12.754%	$162.7829	$162.78	$162.80	$162.80
Purchase #2	$77.53	11.551%	$86.4855	$86.49	$86.50	$86.50
Purchase #3	$133.74	4.839%	$140.2117	$140.21	$140.20	$140.20
Purchase #4	$203.86	6.410%	$216.9274	$216.93	$216.95	$216.90
Purchase #5	$232.72	4.307%	$242.7433	$242.74	$242.75	$242.70
Purchase #6	$75.35	4.771%	$78.9449	$78.94	$78.95	$78.90
Purchase #7	$87.63	4.564%	$91.6294	$91.63	$91.65	$91.60
7 purchase totals =	$955.20		$1,019.7251	$1,019.72	$1,019.80	$1,019.60