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	$249.89	9.344%	$273.2397	$273.24	$273.25	$273.20
Purchase #2	$187.49	6.851%	$200.3349	$200.33	$200.35	$200.30
Purchase #3	$99.95	3.700%	$103.6482	$103.65	$103.65	$103.60
Purchase #4	$177.46	7.837%	$191.3675	$191.37	$191.35	$191.40
Purchase #5	$71.79	7.108%	$76.8928	$76.89	$76.90	$76.90
Purchase #6	$76.50	9.177%	$83.5204	$83.52	$83.50	$83.50
Purchase #7	$141.59	12.447%	$159.2137	$159.21	$159.20	$159.20
7 purchase totals =	$1,004.67		$1,088.2172	$1,088.21	$1,088.20	$1,088.10