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	$31.46	7.568%	$33.8409	$33.84	$33.85	$33.80
Purchase #2	$187.56	4.811%	$196.5835	$196.58	$196.60	$196.60
Purchase #3	$112.72	11.167%	$125.3074	$125.31	$125.30	$125.30
Purchase #4	$122.70	11.512%	$136.8252	$136.83	$136.85	$136.80
Purchase #5	$39.33	3.638%	$40.7608	$40.76	$40.75	$40.80
Purchase #6	$189.50	11.288%	$210.8908	$210.89	$210.90	$210.90
Purchase #7	$87.81	10.862%	$97.3479	$97.35	$97.35	$97.30
7 purchase totals =	$771.08		$841.5565	$841.56	$841.60	$841.50