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	$246.67	13.409%	$279.746	$279.75	$279.75	$279.70
Purchase #2	$203.59	5.796%	$215.3901	$215.39	$215.40	$215.40
Purchase #3	$50.77	13.759%	$57.7554	$57.76	$57.75	$57.80
Purchase #4	$208.33	4.544%	$217.7965	$217.80	$217.80	$217.80
Purchase #5	$163.73	13.799%	$186.3231	$186.32	$186.30	$186.30
Purchase #6	$164.34	4.478%	$171.6991	$171.70	$171.70	$171.70
Purchase #7	$158.31	8.369%	$171.559	$171.56	$171.55	$171.60
7 purchase totals =	$1,195.74		$1,300.2692	$1,300.28	$1,300.25	$1,300.30