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	$137.53	3.822%	$142.7864	$142.79	$142.80	$142.80
Purchase #2	$184.72	6.308%	$196.3721	$196.37	$196.35	$196.40
Purchase #3	$190.77	9.693%	$209.2613	$209.26	$209.25	$209.30
Purchase #4	$162.57	12.365%	$182.6718	$182.67	$182.65	$182.70
Purchase #5	$33.43	13.198%	$37.8421	$37.84	$37.85	$37.80
Purchase #6	$23.83	5.458%	$25.1306	$25.13	$25.15	$25.10
Purchase #7	$203.63	9.667%	$223.3149	$223.31	$223.30	$223.30
7 purchase totals =	$936.48		$1,017.3792	$1,017.37	$1,017.35	$1,017.40