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	$31.54	6.493%	$33.5879	$33.59	$33.60	$33.60
Purchase #2	$59.29	13.492%	$67.2894	$67.29	$67.30	$67.30
Purchase #3	$69.67	3.106%	$71.834	$71.83	$71.85	$71.80
Purchase #4	$249.82	12.606%	$281.3123	$281.31	$281.30	$281.30
Purchase #5	$94.42	13.121%	$106.8088	$106.81	$106.80	$106.80
Purchase #6	$80.68	6.229%	$85.7056	$85.71	$85.70	$85.70
Purchase #7	$164.32	9.742%	$180.3281	$180.33	$180.35	$180.30
7 purchase totals =	$749.74		$826.8661	$826.87	$826.90	$826.80