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	$52.74	13.312%	$59.7607	$59.76	$59.75	$59.80
Purchase #2	$208.81	7.402%	$224.2661	$224.27	$224.25	$224.30
Purchase #3	$153.30	4.583%	$160.3257	$160.33	$160.35	$160.30
Purchase #4	$135.96	3.664%	$140.9416	$140.94	$140.95	$140.90
Purchase #5	$147.28	3.485%	$152.4127	$152.41	$152.40	$152.40
Purchase #6	$27.82	10.177%	$30.6512	$30.65	$30.65	$30.70
Purchase #7	$98.49	12.801%	$111.0977	$111.10	$111.10	$111.10
7 purchase totals =	$824.40		$879.4557	$879.46	$879.45	$879.50