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	$25.86	11.565%	$28.8507	$28.85	$28.85	$28.90
Purchase #2	$250.61	10.366%	$276.5882	$276.59	$276.60	$276.60
Purchase #3	$39.30	8.243%	$42.5395	$42.54	$42.55	$42.50
Purchase #4	$193.96	7.718%	$208.9298	$208.93	$208.95	$208.90
Purchase #5	$131.48	8.793%	$143.041	$143.04	$143.05	$143.00
Purchase #6	$211.51	6.784%	$225.8588	$225.86	$225.85	$225.90
Purchase #7	$91.98	11.266%	$102.3425	$102.34	$102.35	$102.30
7 purchase totals =	$944.70		$1,028.1505	$1,028.15	$1,028.20	$1,028.10