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	$189.37	12.551%	$213.1378	$213.14	$213.15	$213.10
Purchase #2	$159.70	7.503%	$171.6823	$171.68	$171.70	$171.70
Purchase #3	$67.44	4.507%	$70.4795	$70.48	$70.50	$70.50
Purchase #4	$61.59	9.366%	$67.3585	$67.36	$67.35	$67.40
Purchase #5	$10.59	12.261%	$11.8884	$11.89	$11.90	$11.90
Purchase #6	$52.58	8.854%	$57.2354	$57.24	$57.25	$57.20
Purchase #7	$213.94	4.179%	$222.8806	$222.88	$222.90	$222.90
7 purchase totals =	$755.21		$814.6625	$814.67	$814.75	$814.70