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	$171.85	7.710%	$185.0996	$185.10	$185.10	$185.10
Purchase #2	$40.33	7.505%	$43.3568	$43.36	$43.35	$43.40
Purchase #3	$235.67	8.240%	$255.0892	$255.09	$255.10	$255.10
Purchase #4	$192.63	4.809%	$201.8936	$201.89	$201.90	$201.90
Purchase #5	$80.74	10.475%	$89.1975	$89.20	$89.20	$89.20
Purchase #6	$45.86	11.113%	$50.9564	$50.96	$50.95	$51.00
Purchase #7	$203.79	5.814%	$215.6384	$215.64	$215.65	$215.60
7 purchase totals =	$970.87		$1,041.2315	$1,041.24	$1,041.25	$1,041.30