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	$31.36	6.763%	$33.4809	$33.48	$33.50	$33.50
Purchase #2	$150.60	9.405%	$164.7639	$164.76	$164.75	$164.80
Purchase #3	$71.62	11.496%	$79.8534	$79.85	$79.85	$79.90
Purchase #4	$115.93	10.870%	$128.5316	$128.53	$128.55	$128.50
Purchase #5	$238.50	13.471%	$270.6283	$270.63	$270.65	$270.60
Purchase #6	$52.30	4.473%	$54.6394	$54.64	$54.65	$54.60
Purchase #7	$42.62	8.820%	$46.3791	$46.38	$46.40	$46.40
7 purchase totals =	$702.93		$778.2766	$778.27	$778.35	$778.30