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	$72.53	8.606%	$78.7719	$78.77	$78.75	$78.80
Purchase #2	$225.85	6.612%	$240.7832	$240.78	$240.80	$240.80
Purchase #3	$149.83	12.774%	$168.9693	$168.97	$168.95	$169.00
Purchase #4	$169.63	8.407%	$183.8908	$183.89	$183.90	$183.90
Purchase #5	$53.96	5.857%	$57.1204	$57.12	$57.10	$57.10
Purchase #6	$90.26	9.421%	$98.7634	$98.76	$98.75	$98.80
Purchase #7	$47.54	11.481%	$52.9981	$53.00	$53.00	$53.00
7 purchase totals =	$809.60		$881.2971	$881.29	$881.25	$881.40