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	$133.86	5.776%	$141.5918	$141.59	$141.60	$141.60
Purchase #2	$174.51	6.252%	$185.4204	$185.42	$185.40	$185.40
Purchase #3	$100.35	13.484%	$113.8812	$113.88	$113.90	$113.90
Purchase #4	$199.29	9.520%	$218.2624	$218.26	$218.25	$218.30
Purchase #5	$78.98	11.293%	$87.8992	$87.90	$87.90	$87.90
Purchase #6	$33.39	9.144%	$36.4432	$36.44	$36.45	$36.40
Purchase #7	$61.98	9.415%	$67.8154	$67.82	$67.80	$67.80
7 purchase totals =	$782.36		$851.3136	$851.31	$851.30	$851.30