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	$48.36	13.743%	$55.0061	$55.01	$55.00	$55.00
Purchase #2	$249.60	10.492%	$275.788	$275.79	$275.80	$275.80
Purchase #3	$209.38	6.656%	$223.3163	$223.32	$223.30	$223.30
Purchase #4	$84.53	7.520%	$90.8867	$90.89	$90.90	$90.90
Purchase #5	$241.66	13.729%	$274.8375	$274.84	$274.85	$274.80
Purchase #6	$224.41	13.559%	$254.8378	$254.84	$254.85	$254.80
Purchase #7	$59.75	6.617%	$63.7037	$63.70	$63.70	$63.70
7 purchase totals =	$1,117.69		$1,238.3761	$1,238.39	$1,238.40	$1,238.30