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	$47.94	13.119%	$54.2292	$54.23	$54.25	$54.20
Purchase #2	$136.63	4.841%	$143.2443	$143.24	$143.25	$143.20
Purchase #3	$27.54	13.483%	$31.2532	$31.25	$31.25	$31.30
Purchase #4	$184.61	13.159%	$208.9028	$208.90	$208.90	$208.90
Purchase #5	$28.76	10.725%	$31.8445	$31.84	$31.85	$31.80
Purchase #6	$213.55	10.568%	$236.118	$236.12	$236.10	$236.10
Purchase #7	$196.37	11.319%	$218.5971	$218.60	$218.60	$218.60
7 purchase totals =	$835.40		$924.1891	$924.18	$924.20	$924.10