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	$135.87	5.791%	$143.7382	$143.74	$143.75	$143.70
Purchase #2	$80.69	12.119%	$90.4688	$90.47	$90.45	$90.50
Purchase #3	$189.57	10.398%	$209.2815	$209.28	$209.30	$209.30
Purchase #4	$24.31	12.378%	$27.3191	$27.32	$27.30	$27.30
Purchase #5	$222.56	10.440%	$245.7953	$245.80	$245.80	$245.80
Purchase #6	$35.59	5.816%	$37.6599	$37.66	$37.65	$37.70
Purchase #7	$75.33	12.186%	$84.5097	$84.51	$84.50	$84.50
7 purchase totals =	$763.92		$838.7725	$838.78	$838.75	$838.80