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	$160.54	12.288%	$180.2672	$180.27	$180.25	$180.30
Purchase #2	$98.54	10.446%	$108.8335	$108.83	$108.85	$108.80
Purchase #3	$134.43	9.754%	$147.5423	$147.54	$147.55	$147.50
Purchase #4	$231.36	10.202%	$254.9633	$254.96	$254.95	$255.00
Purchase #5	$31.28	9.681%	$34.3082	$34.31	$34.30	$34.30
Purchase #6	$113.41	12.826%	$127.956	$127.96	$127.95	$128.00
Purchase #7	$196.44	11.492%	$219.0149	$219.01	$219.00	$219.00
7 purchase totals =	$966.00		$1,072.8854	$1,072.88	$1,072.85	$1,072.90