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	$208.27	5.788%	$220.3247	$220.32	$220.30	$220.30
Purchase #2	$41.70	4.225%	$43.4618	$43.46	$43.45	$43.50
Purchase #3	$92.83	7.764%	$100.0373	$100.04	$100.05	$100.00
Purchase #4	$118.86	12.140%	$133.2896	$133.29	$133.30	$133.30
Purchase #5	$173.74	3.817%	$180.3717	$180.37	$180.35	$180.40
Purchase #6	$168.94	7.775%	$182.0751	$182.08	$182.10	$182.10
Purchase #7	$222.56	12.556%	$250.5046	$250.50	$250.50	$250.50
7 purchase totals =	$1,026.90		$1,110.0648	$1,110.06	$1,110.05	$1,110.10