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	$28.44	5.474%	$29.9968	$30.00	$30.00	$30.00
Purchase #2	$105.81	5.218%	$111.3312	$111.33	$111.35	$111.30
Purchase #3	$84.40	7.301%	$90.562	$90.56	$90.55	$90.60
Purchase #4	$176.30	3.818%	$183.0311	$183.03	$183.05	$183.00
Purchase #5	$192.59	3.271%	$198.8896	$198.89	$198.90	$198.90
Purchase #6	$183.50	6.211%	$194.8972	$194.90	$194.90	$194.90
Purchase #7	$160.64	4.613%	$168.0503	$168.05	$168.05	$168.10
7 purchase totals =	$931.68		$976.7582	$976.76	$976.80	$976.80