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	$160.59	11.489%	$179.0402	$179.04	$179.05	$179.00
Purchase #2	$140.68	10.437%	$155.3628	$155.36	$155.35	$155.40
Purchase #3	$113.65	9.680%	$124.6513	$124.65	$124.65	$124.70
Purchase #4	$117.89	5.118%	$123.9236	$123.92	$123.90	$123.90
Purchase #5	$55.81	8.738%	$60.6867	$60.69	$60.70	$60.70
Purchase #6	$216.47	12.520%	$243.572	$243.57	$243.55	$243.60
Purchase #7	$80.66	11.467%	$89.9093	$89.91	$89.90	$89.90
7 purchase totals =	$885.75		$977.1459	$977.14	$977.10	$977.20