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	$80.45	12.356%	$90.3904	$90.39	$90.40	$90.40
Purchase #2	$169.47	13.438%	$192.2434	$192.24	$192.25	$192.20
Purchase #3	$231.88	3.868%	$240.8491	$240.85	$240.85	$240.80
Purchase #4	$28.64	9.360%	$31.3207	$31.32	$31.30	$31.30
Purchase #5	$220.60	8.802%	$240.0172	$240.02	$240.00	$240.00
Purchase #6	$98.75	6.586%	$105.2537	$105.25	$105.25	$105.30
Purchase #7	$190.46	7.394%	$204.5426	$204.54	$204.55	$204.50
7 purchase totals =	$1,020.25		$1,104.6171	$1,104.61	$1,104.60	$1,104.50