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	$67.55	6.206%	$71.7422	$71.74	$71.75	$71.70
Purchase #2	$85.31	7.726%	$91.9011	$91.90	$91.90	$91.90
Purchase #3	$57.89	5.113%	$60.8499	$60.85	$60.85	$60.80
Purchase #4	$79.70	7.118%	$85.373	$85.37	$85.35	$85.40
Purchase #5	$77.49	3.249%	$80.0077	$80.01	$80.00	$80.00
Purchase #6	$237.59	12.750%	$267.8827	$267.88	$267.90	$267.90
Purchase #7	$43.31	10.566%	$47.8861	$47.89	$47.90	$47.90
7 purchase totals =	$648.84		$705.6427	$705.64	$705.65	$705.60