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	$180.36	4.712%	$188.8586	$188.86	$188.85	$188.90
Purchase #2	$32.62	9.481%	$35.7127	$35.71	$35.70	$35.70
Purchase #3	$79.39	12.368%	$89.209	$89.21	$89.20	$89.20
Purchase #4	$245.94	12.510%	$276.7071	$276.71	$276.70	$276.70
Purchase #5	$43.41	4.160%	$45.2159	$45.22	$45.20	$45.20
Purchase #6	$34.68	9.287%	$37.9007	$37.90	$37.90	$37.90
Purchase #7	$25.53	10.831%	$28.2952	$28.30	$28.30	$28.30
7 purchase totals =	$641.93		$701.8992	$701.91	$701.85	$701.90