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	$138.40	12.149%	$155.2142	$155.21	$155.20	$155.20
Purchase #2	$65.79	10.645%	$72.7933	$72.79	$72.80	$72.80
Purchase #3	$243.67	6.111%	$258.5607	$258.56	$258.55	$258.60
Purchase #4	$66.80	5.331%	$70.3611	$70.36	$70.35	$70.40
Purchase #5	$161.39	10.360%	$178.11	$178.11	$178.10	$178.10
Purchase #6	$75.65	3.521%	$78.3136	$78.31	$78.30	$78.30
Purchase #7	$152.72	12.147%	$171.2709	$171.27	$171.25	$171.30
7 purchase totals =	$904.42		$984.6238	$984.61	$984.55	$984.70