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	$122.46	13.414%	$138.8868	$138.89	$138.90	$138.90
Purchase #2	$88.30	12.507%	$99.3437	$99.34	$99.35	$99.30
Purchase #3	$91.93	8.818%	$100.0364	$100.04	$100.05	$100.00
Purchase #4	$216.47	13.515%	$245.7259	$245.73	$245.75	$245.70
Purchase #5	$106.86	3.856%	$110.9805	$110.98	$111.00	$111.00
Purchase #6	$180.44	4.128%	$187.8886	$187.89	$187.90	$187.90
Purchase #7	$239.98	11.628%	$267.8849	$267.88	$267.90	$267.90
7 purchase totals =	$1,046.44		$1,150.7468	$1,150.75	$1,150.85	$1,150.70