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	$10.53	3.615%	$10.9107	$10.91	$10.90	$10.90
Purchase #2	$219.91	13.813%	$250.2862	$250.29	$250.30	$250.30
Purchase #3	$101.70	6.458%	$108.2678	$108.27	$108.25	$108.30
Purchase #4	$41.85	7.576%	$45.0206	$45.02	$45.00	$45.00
Purchase #5	$168.83	11.113%	$187.5921	$187.59	$187.60	$187.60
Purchase #6	$28.79	12.518%	$32.3939	$32.39	$32.40	$32.40
Purchase #7	$86.99	7.524%	$93.5351	$93.54	$93.55	$93.50
7 purchase totals =	$658.60		$728.0064	$728.01	$728.00	$728.00