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	$160.86	12.756%	$181.3793	$181.38	$181.40	$181.40
Purchase #2	$84.98	9.260%	$92.8491	$92.85	$92.85	$92.80
Purchase #3	$171.26	10.229%	$188.7782	$188.78	$188.80	$188.80
Purchase #4	$195.73	6.364%	$208.1863	$208.19	$208.20	$208.20
Purchase #5	$85.91	3.761%	$89.1411	$89.14	$89.15	$89.10
Purchase #6	$77.63	13.217%	$87.8904	$87.89	$87.90	$87.90
Purchase #7	$81.89	12.526%	$92.1475	$92.15	$92.15	$92.10
7 purchase totals =	$858.26		$940.3719	$940.38	$940.45	$940.30