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	$37.96	11.633%	$42.3759	$42.38	$42.40	$42.40
Purchase #2	$91.48	10.273%	$100.8777	$100.88	$100.90	$100.90
Purchase #3	$160.25	6.800%	$171.147	$171.15	$171.15	$171.10
Purchase #4	$161.87	4.700%	$169.4779	$169.48	$169.50	$169.50
Purchase #5	$179.77	3.166%	$185.4615	$185.46	$185.45	$185.50
Purchase #6	$116.64	7.754%	$125.6843	$125.68	$125.70	$125.70
Purchase #7	$101.38	9.689%	$111.2027	$111.20	$111.20	$111.20
7 purchase totals =	$849.35		$906.2270	$906.23	$906.30	$906.30