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	$112.35	4.614%	$117.5338	$117.53	$117.55	$117.50
Purchase #2	$138.70	11.862%	$155.1526	$155.15	$155.15	$155.20
Purchase #3	$163.62	4.825%	$171.5147	$171.51	$171.50	$171.50
Purchase #4	$180.54	8.502%	$195.8895	$195.89	$195.90	$195.90
Purchase #5	$73.42	11.850%	$82.1203	$82.12	$82.10	$82.10
Purchase #6	$242.37	12.308%	$272.2009	$272.20	$272.20	$272.20
Purchase #7	$9.39	11.630%	$10.4821	$10.48	$10.50	$10.50
7 purchase totals =	$920.39		$1,004.8939	$1,004.88	$1,004.90	$1,004.90