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	$64.80	11.499%	$72.2514	$72.25	$72.25	$72.30
Purchase #2	$125.87	8.673%	$136.7867	$136.79	$136.80	$136.80
Purchase #3	$107.41	11.771%	$120.0532	$120.05	$120.05	$120.10
Purchase #4	$220.72	9.589%	$241.8848	$241.88	$241.90	$241.90
Purchase #5	$31.78	5.588%	$33.5559	$33.56	$33.55	$33.60
Purchase #6	$98.75	13.212%	$111.7969	$111.80	$111.80	$111.80
Purchase #7	$18.67	7.400%	$20.0516	$20.05	$20.05	$20.10
7 purchase totals =	$668.00		$736.3805	$736.38	$736.40	$736.60