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	$73.37	7.369%	$78.7766	$78.78	$78.80	$78.80
Purchase #2	$185.54	12.473%	$208.6824	$208.68	$208.70	$208.70
Purchase #3	$83.78	7.357%	$89.9437	$89.94	$89.95	$89.90
Purchase #4	$125.33	4.597%	$131.0914	$131.09	$131.10	$131.10
Purchase #5	$126.40	11.140%	$140.481	$140.48	$140.50	$140.50
Purchase #6	$249.57	8.192%	$270.0148	$270.01	$270.00	$270.00
Purchase #7	$225.35	12.796%	$254.1858	$254.19	$254.20	$254.20
7 purchase totals =	$1,069.34		$1,173.1757	$1,173.17	$1,173.25	$1,173.20