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	$39.25	5.287%	$41.3251	$41.33	$41.35	$41.30
Purchase #2	$250.42	9.132%	$273.2884	$273.29	$273.30	$273.30
Purchase #3	$92.25	7.785%	$99.4317	$99.43	$99.45	$99.40
Purchase #4	$101.94	5.167%	$107.2072	$107.21	$107.20	$107.20
Purchase #5	$49.79	7.329%	$53.4391	$53.44	$53.45	$53.40
Purchase #6	$112.89	9.221%	$123.2996	$123.30	$123.30	$123.30
Purchase #7	$137.99	5.450%	$145.5105	$145.51	$145.50	$145.50
7 purchase totals =	$784.53		$843.5016	$843.51	$843.55	$843.40