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	$45.73	12.640%	$51.5103	$51.51	$51.50	$51.50
Purchase #2	$246.69	9.643%	$270.4783	$270.48	$270.50	$270.50
Purchase #3	$57.38	7.510%	$61.6892	$61.69	$61.70	$61.70
Purchase #4	$59.77	9.378%	$65.3752	$65.38	$65.40	$65.40
Purchase #5	$154.89	6.413%	$164.8231	$164.82	$164.80	$164.80
Purchase #6	$125.52	6.228%	$133.3374	$133.34	$133.35	$133.30
Purchase #7	$243.86	12.356%	$273.9913	$273.99	$274.00	$274.00
7 purchase totals =	$933.84		$1,021.2048	$1,021.21	$1,021.25	$1,021.20