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	$57.64	5.292%	$60.6903	$60.69	$60.70	$60.70
Purchase #2	$215.55	7.372%	$231.4403	$231.44	$231.45	$231.40
Purchase #3	$92.31	12.309%	$103.6724	$103.67	$103.65	$103.70
Purchase #4	$52.63	5.363%	$55.4525	$55.45	$55.45	$55.50
Purchase #5	$92.57	7.628%	$99.6312	$99.63	$99.65	$99.60
Purchase #6	$101.50	5.354%	$106.9343	$106.93	$106.95	$106.90
Purchase #7	$131.29	7.404%	$141.0107	$141.01	$141.00	$141.00
7 purchase totals =	$743.49		$798.8317	$798.82	$798.85	$798.80