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	$31.28	7.271%	$33.5544	$33.55	$33.55	$33.60
Purchase #2	$222.37	12.652%	$250.5043	$250.50	$250.50	$250.50
Purchase #3	$103.86	11.484%	$115.7873	$115.79	$115.80	$115.80
Purchase #4	$120.45	6.751%	$128.5816	$128.58	$128.60	$128.60
Purchase #5	$202.50	13.261%	$229.3535	$229.35	$229.35	$229.40
Purchase #6	$139.89	6.121%	$148.4527	$148.45	$148.45	$148.50
Purchase #7	$5.82	13.442%	$6.6023	$6.60	$6.60	$6.60
7 purchase totals =	$826.17		$912.8361	$912.82	$912.85	$913.00