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	$18.56	10.678%	$20.5418	$20.54	$20.55	$20.50
Purchase #2	$69.73	4.637%	$72.9634	$72.96	$72.95	$73.00
Purchase #3	$201.28	8.714%	$218.8195	$218.82	$218.80	$218.80
Purchase #4	$135.93	4.332%	$141.8185	$141.82	$141.80	$141.80
Purchase #5	$113.53	13.222%	$128.5409	$128.54	$128.55	$128.50
Purchase #6	$31.46	10.598%	$34.7941	$34.79	$34.80	$34.80
Purchase #7	$126.38	4.103%	$131.5654	$131.57	$131.55	$131.60
7 purchase totals =	$696.87		$749.0436	$749.04	$749.00	$749.00