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	$54.67	9.360%	$59.7871	$59.79	$59.80	$59.80
Purchase #2	$152.87	10.281%	$168.5866	$168.59	$168.60	$168.60
Purchase #3	$29.51	8.306%	$31.9611	$31.96	$31.95	$32.00
Purchase #4	$84.63	10.746%	$93.7243	$93.72	$93.70	$93.70
Purchase #5	$55.90	3.686%	$57.9605	$57.96	$57.95	$58.00
Purchase #6	$186.98	12.231%	$209.8495	$209.85	$209.85	$209.80
Purchase #7	$104.83	8.604%	$113.8496	$113.85	$113.85	$113.80
7 purchase totals =	$669.39		$735.7187	$735.72	$735.70	$735.70