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	$73.72	6.534%	$78.5369	$78.54	$78.55	$78.50
Purchase #2	$93.82	10.130%	$103.324	$103.32	$103.30	$103.30
Purchase #3	$196.37	10.605%	$217.195	$217.20	$217.20	$217.20
Purchase #4	$47.58	6.265%	$50.5609	$50.56	$50.55	$50.60
Purchase #5	$109.39	9.585%	$119.875	$119.88	$119.90	$119.90
Purchase #6	$94.57	4.448%	$98.7765	$98.78	$98.80	$98.80
Purchase #7	$50.41	9.821%	$55.3608	$55.36	$55.35	$55.40
7 purchase totals =	$665.86		$723.6291	$723.64	$723.65	$723.70