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	$202.99	8.833%	$220.9201	$220.92	$220.90	$220.90
Purchase #2	$135.56	8.697%	$147.3497	$147.35	$147.35	$147.30
Purchase #3	$83.57	3.289%	$86.3186	$86.32	$86.30	$86.30
Purchase #4	$38.26	6.770%	$40.8502	$40.85	$40.85	$40.90
Purchase #5	$69.31	4.610%	$72.5052	$72.51	$72.50	$72.50
Purchase #6	$49.43	11.794%	$55.2598	$55.26	$55.25	$55.30
Purchase #7	$129.70	5.718%	$137.1162	$137.12	$137.10	$137.10
7 purchase totals =	$708.82		$760.3198	$760.33	$760.25	$760.30