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	$170.46	4.591%	$178.2858	$178.29	$178.30	$178.30
Purchase #2	$105.84	3.853%	$109.918	$109.92	$109.90	$109.90
Purchase #3	$63.48	11.757%	$70.9433	$70.94	$70.95	$70.90
Purchase #4	$185.70	7.421%	$199.4808	$199.48	$199.50	$199.50
Purchase #5	$93.25	12.768%	$105.1562	$105.16	$105.15	$105.20
Purchase #6	$196.63	12.740%	$221.6807	$221.68	$221.70	$221.70
Purchase #7	$64.61	10.801%	$71.5885	$71.59	$71.60	$71.60
7 purchase totals =	$879.97		$957.0533	$957.06	$957.10	$957.10