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	$25.95	5.228%	$27.3067	$27.31	$27.30	$27.30
Purchase #2	$28.50	5.259%	$29.9988	$30.00	$30.00	$30.00
Purchase #3	$38.64	10.854%	$42.834	$42.83	$42.85	$42.80
Purchase #4	$56.88	10.659%	$62.9428	$62.94	$62.95	$62.90
Purchase #5	$133.90	12.731%	$150.9468	$150.95	$150.95	$150.90
Purchase #6	$239.89	10.417%	$264.8793	$264.88	$264.90	$264.90
Purchase #7	$50.34	10.735%	$55.744	$55.74	$55.75	$55.70
7 purchase totals =	$574.10		$634.6524	$634.65	$634.70	$634.50