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	$95.93	9.334%	$104.8841	$104.88	$104.90	$104.90
Purchase #2	$64.98	3.819%	$67.4616	$67.46	$67.45	$67.50
Purchase #3	$159.27	6.763%	$170.0414	$170.04	$170.05	$170.00
Purchase #4	$180.92	3.290%	$186.8723	$186.87	$186.85	$186.90
Purchase #5	$216.48	3.853%	$224.821	$224.82	$224.80	$224.80
Purchase #6	$222.73	11.821%	$249.0589	$249.06	$249.05	$249.10
Purchase #7	$42.85	9.392%	$46.8745	$46.87	$46.85	$46.90
7 purchase totals =	$983.16		$1,050.0138	$1,050.00	$1,049.95	$1,050.10