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	$218.62	12.315%	$245.5431	$245.54	$245.55	$245.50
Purchase #2	$244.72	8.578%	$265.7121	$265.71	$265.70	$265.70
Purchase #3	$83.92	7.518%	$90.2291	$90.23	$90.25	$90.20
Purchase #4	$5.79	12.570%	$6.5178	$6.52	$6.50	$6.50
Purchase #5	$6.58	13.714%	$7.4824	$7.48	$7.50	$7.50
Purchase #6	$35.39	11.484%	$39.4542	$39.45	$39.45	$39.50
Purchase #7	$196.83	8.618%	$213.7928	$213.79	$213.80	$213.80
7 purchase totals =	$791.85		$868.7315	$868.72	$868.75	$868.70