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	$223.59	3.744%	$231.9612	$231.96	$231.95	$232.00
Purchase #2	$109.72	6.146%	$116.4634	$116.46	$116.45	$116.50
Purchase #3	$59.95	8.363%	$64.9636	$64.96	$64.95	$65.00
Purchase #4	$156.56	5.299%	$164.8561	$164.86	$164.85	$164.90
Purchase #5	$156.29	7.744%	$168.3931	$168.39	$168.40	$168.40
Purchase #6	$47.37	13.831%	$53.9217	$53.92	$53.90	$53.90
Purchase #7	$154.26	4.228%	$160.7821	$160.78	$160.80	$160.80
7 purchase totals =	$907.74		$961.3412	$961.33	$961.30	$961.50