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	$70.28	3.526%	$72.7581	$72.76	$72.75	$72.80
Purchase #2	$104.75	6.310%	$111.3597	$111.36	$111.35	$111.40
Purchase #3	$181.90	4.392%	$189.889	$189.89	$189.90	$189.90
Purchase #4	$172.44	10.502%	$190.5496	$190.55	$190.55	$190.50
Purchase #5	$140.87	7.133%	$150.9183	$150.92	$150.90	$150.90
Purchase #6	$208.38	11.688%	$232.7355	$232.74	$232.75	$232.70
Purchase #7	$36.81	11.816%	$41.1595	$41.16	$41.15	$41.20
7 purchase totals =	$915.43		$989.3697	$989.38	$989.35	$989.40