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	$139.48	12.400%	$156.7755	$156.78	$156.80	$156.80
Purchase #2	$113.51	7.324%	$121.8235	$121.82	$121.80	$121.80
Purchase #3	$84.87	7.242%	$91.0163	$91.02	$91.00	$91.00
Purchase #4	$31.75	3.624%	$32.9006	$32.90	$32.90	$32.90
Purchase #5	$41.57	12.360%	$46.7081	$46.71	$46.70	$46.70
Purchase #6	$97.63	3.199%	$100.7532	$100.75	$100.75	$100.80
Purchase #7	$98.57	6.873%	$105.3447	$105.34	$105.35	$105.30
7 purchase totals =	$607.38		$655.3219	$655.32	$655.30	$655.30