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	$89.33	12.661%	$100.6401	$100.64	$100.65	$100.60
Purchase #2	$160.64	9.774%	$176.341	$176.34	$176.35	$176.30
Purchase #3	$131.92	6.322%	$140.26	$140.26	$140.25	$140.30
Purchase #4	$165.35	12.153%	$185.445	$185.45	$185.45	$185.40
Purchase #5	$73.83	13.440%	$83.7528	$83.75	$83.75	$83.80
Purchase #6	$108.99	13.362%	$123.5532	$123.55	$123.55	$123.60
Purchase #7	$102.57	13.263%	$116.1739	$116.17	$116.15	$116.20
7 purchase totals =	$832.63		$926.1660	$926.16	$926.15	$926.20