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	$31.86	6.388%	$33.8952	$33.90	$33.90	$33.90
Purchase #2	$223.27	6.549%	$237.892	$237.89	$237.90	$237.90
Purchase #3	$232.78	4.176%	$242.5009	$242.50	$242.50	$242.50
Purchase #4	$152.91	12.166%	$171.513	$171.51	$171.50	$171.50
Purchase #5	$184.98	12.292%	$207.7177	$207.72	$207.70	$207.70
Purchase #6	$115.28	13.654%	$131.0203	$131.02	$131.00	$131.00
Purchase #7	$101.35	5.587%	$107.0124	$107.01	$107.00	$107.00
7 purchase totals =	$1,042.43		$1,131.5515	$1,131.55	$1,131.50	$1,131.50