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	$41.40	8.469%	$44.9062	$44.91	$44.90	$44.90
Purchase #2	$41.92	9.161%	$45.7603	$45.76	$45.75	$45.80
Purchase #3	$58.93	10.146%	$64.909	$64.91	$64.90	$64.90
Purchase #4	$223.89	9.585%	$245.3499	$245.35	$245.35	$245.30
Purchase #5	$75.54	6.435%	$80.401	$80.40	$80.40	$80.40
Purchase #6	$85.42	5.587%	$90.1924	$90.19	$90.20	$90.20
Purchase #7	$84.68	9.112%	$92.396	$92.40	$92.40	$92.40
7 purchase totals =	$611.78		$663.9148	$663.92	$663.90	$663.90