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	$121.73	3.802%	$126.3582	$126.36	$126.35	$126.40
Purchase #2	$245.45	5.258%	$258.3558	$258.36	$258.35	$258.40
Purchase #3	$153.69	6.770%	$164.0948	$164.09	$164.10	$164.10
Purchase #4	$246.27	10.225%	$271.4511	$271.45	$271.45	$271.50
Purchase #5	$37.41	6.272%	$39.7564	$39.76	$39.75	$39.80
Purchase #6	$110.32	12.211%	$123.7912	$123.79	$123.80	$123.80
Purchase #7	$131.97	5.550%	$139.2943	$139.29	$139.30	$139.30
7 purchase totals =	$1,046.84		$1,123.1018	$1,123.10	$1,123.10	$1,123.30