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	$190.77	6.749%	$203.6451	$203.65	$203.65	$203.60
Purchase #2	$226.48	6.155%	$240.4198	$240.42	$240.40	$240.40
Purchase #3	$179.65	9.600%	$196.8964	$196.90	$196.90	$196.90
Purchase #4	$147.77	9.798%	$162.2485	$162.25	$162.25	$162.20
Purchase #5	$164.72	11.104%	$183.0105	$183.01	$183.00	$183.00
Purchase #6	$80.43	7.218%	$86.2354	$86.24	$86.25	$86.20
Purchase #7	$155.96	10.175%	$171.8289	$171.83	$171.85	$171.80
7 purchase totals =	$1,145.78		$1,244.2846	$1,244.30	$1,244.30	$1,244.10