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	$100.54	12.751%	$113.3599	$113.36	$113.35	$113.40
Purchase #2	$149.54	10.125%	$164.6809	$164.68	$164.70	$164.70
Purchase #3	$198.72	8.498%	$215.6072	$215.61	$215.60	$215.60
Purchase #4	$85.85	3.275%	$88.6616	$88.66	$88.65	$88.70
Purchase #5	$69.87	4.343%	$72.9045	$72.90	$72.90	$72.90
Purchase #6	$32.50	9.506%	$35.5895	$35.59	$35.60	$35.60
Purchase #7	$210.83	10.298%	$232.5413	$232.54	$232.55	$232.50
7 purchase totals =	$847.85		$923.3449	$923.34	$923.35	$923.40