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	$171.88	11.272%	$191.2543	$191.25	$191.25	$191.30
Purchase #2	$130.57	4.872%	$136.9314	$136.93	$136.95	$136.90
Purchase #3	$240.67	8.610%	$261.3917	$261.39	$261.40	$261.40
Purchase #4	$47.87	12.355%	$53.7843	$53.78	$53.80	$53.80
Purchase #5	$173.66	5.866%	$183.8469	$183.85	$183.85	$183.80
Purchase #6	$44.85	3.688%	$46.5041	$46.50	$46.50	$46.50
Purchase #7	$170.34	12.421%	$191.4979	$191.50	$191.50	$191.50
7 purchase totals =	$979.84		$1,065.2106	$1,065.20	$1,065.25	$1,065.20