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	$93.75	6.705%	$100.0359	$100.04	$100.05	$100.00
Purchase #2	$45.51	10.693%	$50.3764	$50.38	$50.40	$50.40
Purchase #3	$246.95	3.738%	$256.181	$256.18	$256.20	$256.20
Purchase #4	$61.29	4.390%	$63.9806	$63.98	$64.00	$64.00
Purchase #5	$92.79	7.652%	$99.8903	$99.89	$99.90	$99.90
Purchase #6	$230.63	6.630%	$245.9208	$245.92	$245.90	$245.90
Purchase #7	$109.74	10.653%	$121.4306	$121.43	$121.45	$121.40
7 purchase totals =	$880.66		$937.8156	$937.82	$937.90	$937.80