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	$103.71	12.441%	$116.6126	$116.61	$116.60	$116.60
Purchase #2	$171.98	12.529%	$193.5274	$193.53	$193.55	$193.50
Purchase #3	$93.80	6.650%	$100.0377	$100.04	$100.05	$100.00
Purchase #4	$130.63	6.697%	$139.3783	$139.38	$139.40	$139.40
Purchase #5	$65.91	11.710%	$73.6281	$73.63	$73.65	$73.60
Purchase #6	$37.90	13.629%	$43.0654	$43.07	$43.05	$43.10
Purchase #7	$34.97	7.226%	$37.4969	$37.50	$37.50	$37.50
7 purchase totals =	$638.90		$703.7464	$703.76	$703.80	$703.70