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	$7.66	7.628%	$8.2443	$8.24	$8.25	$8.20
Purchase #2	$194.69	7.579%	$209.4456	$209.45	$209.45	$209.40
Purchase #3	$59.36	5.298%	$62.5049	$62.50	$62.50	$62.50
Purchase #4	$237.28	13.171%	$268.5321	$268.53	$268.55	$268.50
Purchase #5	$143.79	4.519%	$150.2879	$150.29	$150.30	$150.30
Purchase #6	$98.62	5.228%	$103.7759	$103.78	$103.80	$103.80
Purchase #7	$28.93	8.624%	$31.4249	$31.42	$31.40	$31.40
7 purchase totals =	$770.33		$834.2156	$834.21	$834.25	$834.10