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	$54.61	7.813%	$58.8767	$58.88	$58.90	$58.90
Purchase #2	$166.64	5.789%	$176.2868	$176.29	$176.30	$176.30
Purchase #3	$72.34	11.112%	$80.3784	$80.38	$80.40	$80.40
Purchase #4	$151.51	3.436%	$156.7159	$156.72	$156.70	$156.70
Purchase #5	$154.56	6.502%	$164.6095	$164.61	$164.60	$164.60
Purchase #6	$152.48	6.554%	$162.4735	$162.47	$162.45	$162.50
Purchase #7	$193.99	5.350%	$204.3685	$204.37	$204.35	$204.40
7 purchase totals =	$946.13		$1,003.7093	$1,003.72	$1,003.70	$1,003.80