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	$102.29	10.669%	$113.2033	$113.20	$113.20	$113.20
Purchase #2	$250.85	12.867%	$283.1269	$283.13	$283.15	$283.10
Purchase #3	$59.63	7.650%	$64.1917	$64.19	$64.20	$64.20
Purchase #4	$82.87	3.651%	$85.8956	$85.90	$85.90	$85.90
Purchase #5	$7.53	3.653%	$7.8051	$7.81	$7.80	$7.80
Purchase #6	$215.30	5.642%	$227.4472	$227.45	$227.45	$227.40
Purchase #7	$39.83	10.257%	$43.9154	$43.92	$43.90	$43.90
7 purchase totals =	$758.30		$825.5852	$825.60	$825.60	$825.50