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	$67.79	8.568%	$73.5982	$73.60	$73.60	$73.60
Purchase #2	$225.94	3.815%	$234.5596	$234.56	$234.55	$234.60
Purchase #3	$136.83	6.157%	$145.2546	$145.25	$145.25	$145.30
Purchase #4	$5.89	7.414%	$6.3267	$6.33	$6.35	$6.30
Purchase #5	$77.76	10.459%	$85.8929	$85.89	$85.90	$85.90
Purchase #6	$69.38	4.452%	$72.4688	$72.47	$72.45	$72.50
Purchase #7	$161.86	11.219%	$180.0191	$180.02	$180.00	$180.00
7 purchase totals =	$745.45		$798.1199	$798.12	$798.10	$798.20