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	$25.66	7.221%	$27.5129	$27.51	$27.50	$27.50
Purchase #2	$41.53	13.187%	$47.0066	$47.01	$47.00	$47.00
Purchase #3	$163.99	6.856%	$175.2332	$175.23	$175.25	$175.20
Purchase #4	$211.47	7.352%	$227.0173	$227.02	$227.00	$227.00
Purchase #5	$226.57	7.393%	$243.3203	$243.32	$243.30	$243.30
Purchase #6	$176.71	11.401%	$196.8567	$196.86	$196.85	$196.90
Purchase #7	$170.44	7.545%	$183.2997	$183.30	$183.30	$183.30
7 purchase totals =	$1,016.37		$1,100.2467	$1,100.25	$1,100.20	$1,100.20