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	$113.89	3.504%	$117.8807	$117.88	$117.90	$117.90
Purchase #2	$225.87	13.211%	$255.7097	$255.71	$255.70	$255.70
Purchase #3	$17.41	10.269%	$19.1978	$19.20	$19.20	$19.20
Purchase #4	$245.53	7.421%	$263.7508	$263.75	$263.75	$263.80
Purchase #5	$57.72	3.722%	$59.8683	$59.87	$59.85	$59.90
Purchase #6	$94.33	10.178%	$103.9309	$103.93	$103.95	$103.90
Purchase #7	$30.54	9.809%	$33.5357	$33.54	$33.55	$33.50
7 purchase totals =	$785.29		$853.8739	$853.88	$853.90	$853.90