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	$153.42	9.770%	$168.4091	$168.41	$168.40	$168.40
Purchase #2	$187.80	11.812%	$209.9829	$209.98	$210.00	$210.00
Purchase #3	$178.98	6.339%	$190.3255	$190.33	$190.35	$190.30
Purchase #4	$29.93	4.781%	$31.361	$31.36	$31.35	$31.40
Purchase #5	$105.42	10.392%	$116.3752	$116.38	$116.40	$116.40
Purchase #6	$20.43	7.722%	$22.0076	$22.01	$22.00	$22.00
Purchase #7	$90.26	6.361%	$96.0014	$96.00	$96.00	$96.00
7 purchase totals =	$766.24		$834.4627	$834.47	$834.50	$834.50