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	$90.90	6.484%	$96.794	$96.79	$96.80	$96.80
Purchase #2	$152.74	4.309%	$159.3216	$159.32	$159.30	$159.30
Purchase #3	$95.31	4.471%	$99.5713	$99.57	$99.55	$99.60
Purchase #4	$162.69	5.441%	$171.542	$171.54	$171.55	$171.50
Purchase #5	$88.31	13.798%	$100.495	$100.50	$100.50	$100.50
Purchase #6	$76.95	4.202%	$80.1834	$80.18	$80.20	$80.20
Purchase #7	$108.48	7.330%	$116.4316	$116.43	$116.45	$116.40
7 purchase totals =	$775.38		$824.3389	$824.33	$824.35	$824.30