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	$160.54	12.252%	$180.2094	$180.21	$180.20	$180.20
Purchase #2	$175.90	11.639%	$196.373	$196.37	$196.35	$196.40
Purchase #3	$117.50	8.860%	$127.9105	$127.91	$127.90	$127.90
Purchase #4	$216.54	11.159%	$240.7037	$240.70	$240.70	$240.70
Purchase #5	$145.67	12.752%	$164.2458	$164.25	$164.25	$164.20
Purchase #6	$174.76	13.801%	$198.8786	$198.88	$198.90	$198.90
Purchase #7	$92.41	12.751%	$104.1932	$104.19	$104.20	$104.20
7 purchase totals =	$1,083.32		$1,212.5142	$1,212.51	$1,212.50	$1,212.50