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	$31.30	9.645%	$34.3189	$34.32	$34.30	$34.30
Purchase #2	$196.51	13.706%	$223.4437	$223.44	$223.45	$223.40
Purchase #3	$168.86	13.303%	$191.3234	$191.32	$191.30	$191.30
Purchase #4	$74.38	11.356%	$82.8266	$82.83	$82.85	$82.80
Purchase #5	$37.99	8.637%	$41.2712	$41.27	$41.25	$41.30
Purchase #6	$185.28	13.626%	$210.5263	$210.53	$210.55	$210.50
Purchase #7	$205.65	9.609%	$225.4109	$225.41	$225.40	$225.40
7 purchase totals =	$899.97		$1,009.1210	$1,009.12	$1,009.10	$1,009.00