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	$84.40	9.592%	$92.4956	$92.50	$92.50	$92.50
Purchase #2	$220.85	11.327%	$245.8657	$245.87	$245.85	$245.90
Purchase #3	$57.63	12.138%	$64.6251	$64.63	$64.65	$64.60
Purchase #4	$248.54	13.628%	$282.411	$282.41	$282.40	$282.40
Purchase #5	$59.40	4.712%	$62.1989	$62.20	$62.20	$62.20
Purchase #6	$78.94	4.524%	$82.5112	$82.51	$82.50	$82.50
Purchase #7	$82.57	5.299%	$86.9454	$86.95	$86.95	$86.90
7 purchase totals =	$832.33		$917.0529	$917.07	$917.05	$917.00