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	$153.30	3.318%	$158.3865	$158.39	$158.40	$158.40
Purchase #2	$218.73	9.127%	$238.6935	$238.69	$238.70	$238.70
Purchase #3	$249.46	6.596%	$265.9144	$265.91	$265.90	$265.90
Purchase #4	$92.96	10.707%	$102.9132	$102.91	$102.90	$102.90
Purchase #5	$239.71	8.437%	$259.9343	$259.93	$259.95	$259.90
Purchase #6	$92.98	10.318%	$102.5737	$102.57	$102.55	$102.60
Purchase #7	$86.54	4.566%	$90.4914	$90.49	$90.50	$90.50
7 purchase totals =	$1,133.68		$1,218.9070	$1,218.89	$1,218.90	$1,218.90