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	$237.36	3.285%	$245.1573	$245.16	$245.15	$245.20
Purchase #2	$86.92	6.721%	$92.7619	$92.76	$92.75	$92.80
Purchase #3	$113.90	8.276%	$123.3264	$123.33	$123.35	$123.30
Purchase #4	$80.49	3.823%	$83.5671	$83.57	$83.55	$83.60
Purchase #5	$18.37	9.697%	$20.1513	$20.15	$20.15	$20.20
Purchase #6	$236.61	8.119%	$255.8204	$255.82	$255.80	$255.80
Purchase #7	$152.26	6.652%	$162.3883	$162.39	$162.40	$162.40
7 purchase totals =	$925.91		$983.1727	$983.18	$983.15	$983.30