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	$186.74	6.511%	$198.8986	$198.90	$198.90	$198.90
Purchase #2	$129.34	13.409%	$146.6832	$146.68	$146.70	$146.70
Purchase #3	$246.67	9.568%	$270.2714	$270.27	$270.25	$270.30
Purchase #4	$111.55	4.296%	$116.3422	$116.34	$116.35	$116.30
Purchase #5	$40.94	11.537%	$45.6632	$45.66	$45.65	$45.70
Purchase #6	$142.36	9.127%	$155.3532	$155.35	$155.35	$155.40
Purchase #7	$157.41	9.190%	$171.876	$171.88	$171.90	$171.90
7 purchase totals =	$1,015.01		$1,105.0878	$1,105.08	$1,105.10	$1,105.20