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	$31.56	6.235%	$33.5278	$33.53	$33.55	$33.50
Purchase #2	$109.30	12.769%	$123.2565	$123.26	$123.25	$123.30
Purchase #3	$120.83	12.829%	$136.3313	$136.33	$136.35	$136.30
Purchase #4	$52.88	8.865%	$57.5678	$57.57	$57.55	$57.60
Purchase #5	$213.49	9.551%	$233.8804	$233.88	$233.90	$233.90
Purchase #6	$160.28	6.676%	$170.9803	$170.98	$171.00	$171.00
Purchase #7	$145.72	6.230%	$154.7984	$154.80	$154.80	$154.80
7 purchase totals =	$834.06		$910.3425	$910.35	$910.40	$910.40