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	$52.55	12.604%	$59.1734	$59.17	$59.15	$59.20
Purchase #2	$136.53	7.310%	$146.5103	$146.51	$146.50	$146.50
Purchase #3	$211.74	8.266%	$229.2424	$229.24	$229.25	$229.20
Purchase #4	$135.42	10.780%	$150.0183	$150.02	$150.00	$150.00
Purchase #5	$81.51	13.636%	$92.6247	$92.62	$92.60	$92.60
Purchase #6	$119.35	10.524%	$131.9104	$131.91	$131.90	$131.90
Purchase #7	$189.78	9.359%	$207.5415	$207.54	$207.55	$207.50
7 purchase totals =	$926.88		$1,017.0210	$1,017.01	$1,016.95	$1,016.90