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	$120.59	6.489%	$128.4151	$128.42	$128.40	$128.40
Purchase #2	$142.88	3.116%	$147.3321	$147.33	$147.35	$147.30
Purchase #3	$64.59	13.352%	$73.2141	$73.21	$73.20	$73.20
Purchase #4	$189.46	3.722%	$196.5117	$196.51	$196.50	$196.50
Purchase #5	$82.76	4.508%	$86.4908	$86.49	$86.50	$86.50
Purchase #6	$201.51	7.748%	$217.123	$217.12	$217.10	$217.10
Purchase #7	$77.64	3.649%	$80.4731	$80.47	$80.45	$80.50
7 purchase totals =	$879.43		$929.5599	$929.55	$929.50	$929.50