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	$145.89	12.618%	$164.2984	$164.30	$164.30	$164.30
Purchase #2	$45.90	6.328%	$48.8046	$48.80	$48.80	$48.80
Purchase #3	$31.89	8.168%	$34.4948	$34.49	$34.50	$34.50
Purchase #4	$95.61	3.761%	$99.2059	$99.21	$99.20	$99.20
Purchase #5	$236.80	11.161%	$263.2292	$263.23	$263.25	$263.20
Purchase #6	$109.93	6.741%	$117.3404	$117.34	$117.35	$117.30
Purchase #7	$38.54	12.358%	$43.3028	$43.30	$43.30	$43.30
7 purchase totals =	$704.56		$770.6761	$770.67	$770.70	$770.60