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	$53.40	4.295%	$55.6935	$55.69	$55.70	$55.70
Purchase #2	$80.66	6.525%	$85.9231	$85.92	$85.90	$85.90
Purchase #3	$42.53	10.318%	$46.9182	$46.92	$46.90	$46.90
Purchase #4	$172.41	8.557%	$187.1631	$187.16	$187.15	$187.20
Purchase #5	$67.76	10.817%	$75.0896	$75.09	$75.10	$75.10
Purchase #6	$85.71	10.736%	$94.9118	$94.91	$94.90	$94.90
Purchase #7	$17.59	3.865%	$18.2699	$18.27	$18.25	$18.30
7 purchase totals =	$520.06		$563.9692	$563.96	$563.90	$564.00