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	$26.66	3.854%	$27.6875	$27.69	$27.70	$27.70
Purchase #2	$245.25	6.465%	$261.1054	$261.11	$261.10	$261.10
Purchase #3	$57.74	3.380%	$59.6916	$59.69	$59.70	$59.70
Purchase #4	$86.85	12.294%	$97.5273	$97.53	$97.55	$97.50
Purchase #5	$220.72	12.225%	$247.703	$247.70	$247.70	$247.70
Purchase #6	$215.72	10.693%	$238.7869	$238.79	$238.80	$238.80
Purchase #7	$37.86	13.215%	$42.8632	$42.86	$42.85	$42.90
7 purchase totals =	$890.80		$975.3649	$975.37	$975.40	$975.40