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	$193.73	12.756%	$218.4422	$218.44	$218.45	$218.40
Purchase #2	$23.93	6.157%	$25.4034	$25.40	$25.40	$25.40
Purchase #3	$170.60	8.592%	$185.258	$185.26	$185.25	$185.30
Purchase #4	$235.34	12.800%	$265.4635	$265.46	$265.45	$265.50
Purchase #5	$87.33	10.582%	$96.5713	$96.57	$96.55	$96.60
Purchase #6	$45.33	4.230%	$47.2475	$47.25	$47.25	$47.20
Purchase #7	$151.64	8.775%	$164.9464	$164.95	$164.95	$164.90
7 purchase totals =	$907.90		$1,003.3323	$1,003.33	$1,003.30	$1,003.30