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	$83.69	3.145%	$86.3221	$86.32	$86.30	$86.30
Purchase #2	$116.34	3.241%	$120.1106	$120.11	$120.10	$120.10
Purchase #3	$185.56	5.780%	$196.2854	$196.29	$196.30	$196.30
Purchase #4	$131.98	5.241%	$138.8971	$138.90	$138.90	$138.90
Purchase #5	$111.88	10.817%	$123.9821	$123.98	$124.00	$124.00
Purchase #6	$52.58	7.384%	$56.4625	$56.46	$56.45	$56.50
Purchase #7	$96.28	3.454%	$99.6055	$99.61	$99.60	$99.60
7 purchase totals =	$778.31		$821.6653	$821.67	$821.65	$821.70