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	$31.57	13.356%	$35.7865	$35.79	$35.80	$35.80
Purchase #2	$97.68	6.320%	$103.8534	$103.85	$103.85	$103.90
Purchase #3	$150.43	9.599%	$164.8698	$164.87	$164.85	$164.90
Purchase #4	$50.84	4.281%	$53.0165	$53.02	$53.00	$53.00
Purchase #5	$172.70	9.574%	$189.2343	$189.23	$189.25	$189.20
Purchase #6	$140.44	8.426%	$152.2735	$152.27	$152.25	$152.30
Purchase #7	$164.93	3.740%	$171.0984	$171.10	$171.10	$171.10
7 purchase totals =	$808.59		$870.1324	$870.13	$870.10	$870.20