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	$55.82	3.731%	$57.9026	$57.90	$57.90	$57.90
Purchase #2	$64.51	11.861%	$72.1615	$72.16	$72.15	$72.20
Purchase #3	$28.82	8.611%	$31.3017	$31.30	$31.30	$31.30
Purchase #4	$126.50	3.811%	$131.3209	$131.32	$131.30	$131.30
Purchase #5	$140.85	9.347%	$154.0152	$154.02	$154.00	$154.00
Purchase #6	$181.93	7.653%	$195.8531	$195.85	$195.85	$195.90
Purchase #7	$150.72	6.523%	$160.5515	$160.55	$160.55	$160.60
7 purchase totals =	$749.15		$803.1065	$803.10	$803.05	$803.20